diff --git a/packages/mesh-contract/src/marketplace/offchain.ts b/packages/mesh-contract/src/marketplace/offchain.ts
index f7c5c4b39..a5324508b 100644
--- a/packages/mesh-contract/src/marketplace/offchain.ts
+++ b/packages/mesh-contract/src/marketplace/offchain.ts
@@ -57,6 +57,11 @@ export class MeshMarketplaceContract extends MeshTxInitiator {
     feePercentageBasisPoint: number,
   ) {
     super(inputs);
+    if (feePercentageBasisPoint < 0 || feePercentageBasisPoint > 10000) {
+      throw new Error(
+        `feePercentageBasisPoint must be between 0 and 10000, got ${feePercentageBasisPoint}`,
+      );
+    }
     this.ownerAddress = ownerAddress;
     this.feePercentageBasisPoint = feePercentageBasisPoint;
 
@@ -154,9 +159,14 @@ export class MeshMarketplaceContract extends MeshTxInitiator {
       marketplaceUtxo.output.plutusData!,
     );
 
-    const inputLovelace = marketplaceUtxo.output.amount.find(
+    const lovelaceEntry = marketplaceUtxo.output.amount.find(
       (a) => a.unit === "lovelace",
-    )!.quantity;
+    );
+    if (!lovelaceEntry) {
+      throw new Error(
+        "purchaseAsset: marketplace UTxO is missing a lovelace entry",
+      );
+    }
 
     const tx = this.mesh
       .spendingPlutusScript(this.languageVersion)
@@ -178,27 +188,36 @@ export class MeshMarketplaceContract extends MeshTxInitiator {
       )
       .selectUtxosFrom(utxos);
 
-    let ownerToReceiveLovelace =
-      ((inputDatum.fields[1].int as number) * this.feePercentageBasisPoint) /
-      10000;
-    if (this.feePercentageBasisPoint > 0 && ownerToReceiveLovelace < 1000000) {
-      ownerToReceiveLovelace = 1000000;
+    // Keep all lovelace arithmetic in BigInt to avoid precision loss for
+    // prices above Number.MAX_SAFE_INTEGER (~9M ADA).
+    const priceBig = BigInt(inputDatum.fields[1].int);
+    const feeBig = BigInt(Math.round(this.feePercentageBasisPoint));
+
+    // Ceiling division: (a * b + d - 1) / d mirrors Math.ceil without floats.
+    let ownerToReceiveLovelace = (priceBig * feeBig + 9999n) / 10000n;
+    // Apply 1-ADA minimum only when the listing has a non-zero price; a free
+    // listing (price = 0) should not incur a mandatory fee.
+    if (
+      this.feePercentageBasisPoint > 0 &&
+      priceBig > 0n &&
+      ownerToReceiveLovelace < 1000000n
+    ) {
+      ownerToReceiveLovelace = 1000000n;
     }
 
-    if (ownerToReceiveLovelace > 0) {
+    if (ownerToReceiveLovelace > 0n) {
       const ownerToReceive = [
         {
           unit: "lovelace",
-          quantity: Math.ceil(ownerToReceiveLovelace).toString(),
+          quantity: ownerToReceiveLovelace.toString(),
         },
       ];
       tx.txOut(this.ownerAddress, ownerToReceive);
     }
 
-    const sellerToReceiveLovelace =
-      (inputDatum.fields[1].int as number) + Number(inputLovelace);
+    const sellerToReceiveLovelace = priceBig + BigInt(lovelaceEntry.quantity);
 
-    if (sellerToReceiveLovelace > 0) {
+    if (sellerToReceiveLovelace > 0n) {
       const sellerAddress = serializeAddressObj(
         inputDatum.fields[0],
         this.networkId,
diff --git a/packages/mesh-core-csl/src/offline-providers/offline-evaluator.ts b/packages/mesh-core-csl/src/offline-providers/offline-evaluator.ts
index 628b86036..5fc25e55b 100644
--- a/packages/mesh-core-csl/src/offline-providers/offline-evaluator.ts
+++ b/packages/mesh-core-csl/src/offline-providers/offline-evaluator.ts
@@ -122,14 +122,17 @@ export class OfflineEvaluator implements IEvaluator {
     additionalUtxos: UTxO[],
     additionalTxs: string[],
   ): Promise<Omit<Action, "data">[]> {
-    // Track which utxos is resolved
+    // Work on a copy so the caller's `additionalUtxos` array is never mutated.
+    const resolvedUtxos: UTxO[] = [...additionalUtxos];
+
+    // Track which utxos are resolved
     const foundUtxos = new Set<string>();
 
-    for (const utxo of additionalUtxos) {
+    for (const utxo of resolvedUtxos) {
       foundUtxos.add(`${utxo.input.txHash}:${utxo.input.outputIndex}`);
     }
-    for (const tx of additionalTxs) {
-      const outputs = getTransactionOutputs(tx);
+    for (const additionalTx of additionalTxs) {
+      const outputs = getTransactionOutputs(additionalTx);
       for (const output of outputs) {
         foundUtxos.add(`${output.input.txHash}:${output.input.outputIndex}`);
       }
@@ -138,20 +141,24 @@ export class OfflineEvaluator implements IEvaluator {
       (input) => !foundUtxos.has(`${input.txHash}:${input.outputIndex}`),
     );
     const txHashesSet = new Set(inputsToResolve.map((input) => input.txHash));
-    for (const txHash of txHashesSet) {
-      const utxos = await this.fetcher.fetchUTxOs(txHash);
+
+    // Resolve each distinct parent transaction's UTxOs concurrently.
+    const fetchedUtxoSets = await Promise.all(
+      [...txHashesSet].map((txHash) => this.fetcher.fetchUTxOs(txHash)),
+    );
+    for (const utxos of fetchedUtxoSets) {
       for (const utxo of utxos) {
-        if (utxo)
-          if (
-            inputsToResolve.find(
-              (input) =>
-                input.txHash === txHash &&
-                input.outputIndex === utxo.input.outputIndex,
-            )
-          ) {
-            additionalUtxos.push(utxo);
-            foundUtxos.add(`${utxo.input.txHash}:${utxo.input.outputIndex}`);
-          }
+        if (
+          utxo &&
+          inputsToResolve.some(
+            (input) =>
+              input.txHash === utxo.input.txHash &&
+              input.outputIndex === utxo.input.outputIndex,
+          )
+        ) {
+          resolvedUtxos.push(utxo);
+          foundUtxos.add(`${utxo.input.txHash}:${utxo.input.outputIndex}`);
+        }
       }
     }
     const missing = inputsToResolve.filter(
@@ -167,7 +174,7 @@ export class OfflineEvaluator implements IEvaluator {
     }
     return evaluateTransaction(
       tx,
-      additionalUtxos,
+      resolvedUtxos,
       additionalTxs,
       this.costModels,
       this.slotConfig,
diff --git a/packages/mesh-core-csl/test/offline-providers/evaluator.test.ts b/packages/mesh-core-csl/test/offline-providers/evaluator.test.ts
index 3411e290d..b71390daa 100644
--- a/packages/mesh-core-csl/test/offline-providers/evaluator.test.ts
+++ b/packages/mesh-core-csl/test/offline-providers/evaluator.test.ts
@@ -1,4 +1,4 @@
-import { SLOT_CONFIG_NETWORK } from "@meshsdk/common";
+import { SLOT_CONFIG_NETWORK, UTxO } from "@meshsdk/common";
 import { OfflineEvaluator } from "@meshsdk/core-csl";
 import { OfflineFetcher } from "@meshsdk/provider";
 
@@ -119,7 +119,12 @@ describe("Offline Evaluator", () => {
     };
     fetcher.addUTxOs([utxo_1, utxo_2, utxo_3, utxo_4, utxo_5, utxo_6, utxo_7]);
 
-    const res = await evaluator.evaluateTx(txHex, [], []);
+    // All inputs are resolved from the fetcher (across several parent txs, in
+    // parallel). The caller's array must not be mutated in the process — the
+    // previous implementation pushed the resolved UTxOs into it.
+    const additionalUtxos: UTxO[] = [];
+    const res = await evaluator.evaluateTx(txHex, additionalUtxos, []);
+    expect(additionalUtxos).toHaveLength(0);
     expect(res).toStrictEqual([
       {
         index: 0,