diff --git a/Cargo.lock b/Cargo.lock
index 7df2383..29eb590 100644
--- a/Cargo.lock
+++ b/Cargo.lock
@@ -186,6 +186,7 @@ dependencies = [
 name = "commitment-marketplace"
 version = "0.1.0"
 dependencies = [
+ "shared_utils",
  "soroban-sdk",
 ]
 
diff --git a/contracts/commitment_marketplace/Cargo.toml b/contracts/commitment_marketplace/Cargo.toml
index 5f9a3f2..3918f37 100644
--- a/contracts/commitment_marketplace/Cargo.toml
+++ b/contracts/commitment_marketplace/Cargo.toml
@@ -8,6 +8,7 @@ crate-type = ["cdylib"]
 
 [dependencies]
 soroban-sdk = "21.0.0"
+shared_utils = { path = "../shared_utils" }
 
 [dev-dependencies]
 soroban-sdk = { version = "21.0.0", features = ["testutils"] }
diff --git a/contracts/commitment_marketplace/src/lib.rs b/contracts/commitment_marketplace/src/lib.rs
index 3a5b0e6..3d6e875 100644
--- a/contracts/commitment_marketplace/src/lib.rs
+++ b/contracts/commitment_marketplace/src/lib.rs
@@ -25,6 +25,7 @@ use soroban_sdk::{
     contract, contracterror, contractimpl, contracttype, symbol_short, token, Address, Env, Symbol,
     Vec,
 };
+use shared_utils::math::SafeMath;
 
 // ============================================================================
 // Error Types
@@ -608,9 +609,11 @@ impl CommitmentMarketplace {
                 MarketplaceError::NotInitialized
             })?;
 
-        // Calculate fee and seller proceeds
-        let marketplace_fee = (listing.price * fee_basis_points as i128) / 10000;
-        let seller_proceeds = listing.price - marketplace_fee;
+        // Calculate fee and seller proceeds safely using basis points (bps)
+        let fee_basis_points_i128: i128 = fee_basis_points as i128;
+        let marketplace_fee =
+            SafeMath::div(SafeMath::mul(listing.price, fee_basis_points_i128), 10_000_i128);
+        let seller_proceeds = SafeMath::sub(listing.price, marketplace_fee);
 
         // EFFECTS
         // Remove listing first (prevent reentrancy)
@@ -814,6 +817,13 @@ impl CommitmentMarketplace {
         // CHECKS
         seller.require_auth();
 
+        if seller == offerer {
+            e.storage()
+                .instance()
+                .set(&DataKey::ReentrancyGuard, &false);
+            return Err(MarketplaceError::CannotBuyOwnListing);
+        }
+
         let offers: Vec<Offer> = e
             .storage()
             .persistent()
@@ -1025,7 +1035,10 @@ impl CommitmentMarketplace {
 
         // EFFECTS
         let started_at = e.ledger().timestamp();
-        let ends_at = started_at + duration_seconds;
+        let ends_at = started_at.checked_add(duration_seconds).ok_or_else(|| {
+            e.storage().instance().set(&DataKey::ReentrancyGuard, &false);
+            MarketplaceError::InvalidDuration
+        })?;
 
         let auction = Auction {
             token_id,
@@ -1266,9 +1279,16 @@ impl CommitmentMarketplace {
 
         // INTERACTIONS
         if let Some(winner) = auction.highest_bidder {
-            // Calculate fees
-            let marketplace_fee = (auction.current_bid * fee_basis_points as i128) / 10000;
-            let seller_proceeds = auction.current_bid - marketplace_fee;
+            // Calculate fees safely using basis points (bps, /10_000)
+            let fee_bps = if fee_basis_points > 10_000 {
+                10_000
+            } else {
+                fee_basis_points
+            };
+            let fee_bps_i128 = fee_bps as i128;
+            let marketplace_fee =
+                SafeMath::div(SafeMath::mul(auction.current_bid, fee_bps_i128), 10_000_i128);
+            let seller_proceeds = SafeMath::sub(auction.current_bid, marketplace_fee);
 
             let payment_token_client = token::Client::new(&e, &auction.payment_token);
 
diff --git a/contracts/commitment_marketplace/src/tests.rs b/contracts/commitment_marketplace/src/tests.rs
index d256189..818c474 100644
--- a/contracts/commitment_marketplace/src/tests.rs
+++ b/contracts/commitment_marketplace/src/tests.rs
@@ -323,6 +323,53 @@ fn test_make_duplicate_offer_fails() {
     client.make_offer(&offerer, &1, &600, &payment_token); // Should fail
 }
 
+#[test]
+#[should_panic(expected = "Error(Contract, #8)")] // CannotBuyOwnListing
+fn test_make_offer_own_listing_fails() {
+    let e = Env::default();
+    e.mock_all_auths();
+
+    let (_, _, client) = setup_marketplace(&e);
+
+    let seller = Address::generate(&e);
+    let payment_token = setup_test_token(&e);
+
+    client.list_nft(&seller, &1, &1000, &payment_token);
+    client.make_offer(&seller, &1, &800, &payment_token); // Seller making offer on own listing
+}
+
+#[test]
+#[should_panic(expected = "Error(Contract, #8)")] // CannotBuyOwnListing
+fn test_make_offer_own_auction_fails() {
+    let e = Env::default();
+    e.mock_all_auths();
+
+    let (_, _, client) = setup_marketplace(&e);
+
+    let seller = Address::generate(&e);
+    let payment_token = setup_test_token(&e);
+
+    client.start_auction(&seller, &1, &1000, &86400, &payment_token);
+    client.make_offer(&seller, &1, &1100, &payment_token); // Seller making offer on own auction
+}
+
+#[test]
+#[should_panic(expected = "Error(Contract, #8)")] // CannotBuyOwnListing
+fn test_accept_offer_own_listing_fails() {
+    let e = Env::default();
+    e.mock_all_auths();
+
+    let (_, _, client) = setup_marketplace(&e);
+
+    let seller = Address::generate(&e);
+    let payment_token = setup_test_token(&e);
+
+    client.make_offer(&seller, &1, &1000, &payment_token);
+    client.accept_offer(&seller, &1, &seller); // Seller accepting own offer
+}
+
+
+
 #[test]
 fn test_multiple_offers_same_token() {
     let e = Env::default();