Persistence

struct FMerchantSaveRecord
{
    int32 Version = 1;                      // Save format version
    FGuid MerchantGuid;                     // Unique ID
    TArray<FStockItem> StockItems;          // Stock state
    TArray<FMerchantTransaction> TransactionLog;
    TArray<FGuid> ProcessedNonces;          // Recent nonces
};

FPurchaseQuote Quote = Merchant->QuotePurchase(Player, Item, Qty);

if (!Quote.bSuccess)
{
    switch (Quote.ErrorCode)
    {
        case EMerchantErrorCode::ERR_NO_STOCK:
            DisplayToPlayer("Out of stock! Try again later.");
            break;

        case EMerchantErrorCode::ERR_INSUFFICIENT_FUNDS:
            DisplayToPlayer(FString::Printf(
                "Need %d gold (you have %d)",
                Quote.Total,
                PlayerGold
            ));
            break;

        case EMerchantErrorCode::ERR_INVENTORY_FULL:
            DisplayToPlayer("Inventory full! Free up space.");
            break;

        case EMerchantErrorCode::ERR_OUT_OF_RANGE:
            DisplayToPlayer("Too far from merchant!");
            break;

        default:
            DisplayToPlayer("Cannot complete transaction.");
            break;
    }
    return;
}

// Success - display quote to player
DisplayQuote(Quote);