1. Concrete Example
You buy your suit for $329. The salesperson also gives you a $50 Amazon gift card. In the end, you leave with your suit and a bonus gift. Even if this gift is randomly assigned, it's still a perfectly valid bonus.
2. General Conclusion
Accepting this kind of gift is permissible because:
You only pay the regular price of your product.
The gift is a bonus offered without any strings attached.