Fixes bid price comparison logic in auction handler

Corrects the mathematical comparison for bid price validation to properly compare payment amount against selling amount multiplied by floor price.

Adds clarifying comments explaining the price conversion between tokens and the purpose of MinPriceMultiplier to improve code readability.

x/auction/keeper/auction_type.go

@@ -33,16 +33,19 @@ func fcfsBidHandler(ctx sdk.Context, k Keeper, auction *types.Auction, bid *type
 		)
 	}
 
+	// Note: price converts SellingToken to PaymentToken
+	// Any calculation down the road makes sense only if price is multiplied by a derivative of SellingToken
 	price, err := k.icqoracleKeeper.GetTokenPriceForQuoteDenom(ctx, auction.SellingDenom, auction.PaymentDenom)
 	if err != nil {
 		return err
 	}
 
+	// Apply MinPriceMultiplier
 	bidsFloorPrice := price.Mul(auction.MinPriceMultiplier)
 
-	if bid.SellingTokenAmount.ToLegacyDec().
-		Mul(bidsFloorPrice).
-		LT(bid.PaymentTokenAmount.ToLegacyDec()) {
+	// if paymentAmount < sellingAmount * bidsFloorPrice
+	if bid.PaymentTokenAmount.ToLegacyDec().LT(bid.SellingTokenAmount.ToLegacyDec().
+		Mul(bidsFloorPrice)) {
 		return fmt.Errorf("bid price too low: offered %s%s for %s%s, bids floor price is %s%s (price=%s %s/%s)",
 			bid.PaymentTokenAmount.String(),
 			auction.PaymentDenom,