Limiting # of products user can add


Thanks for taking the time to read my post. I was hoping someone had an idea of how I could limit a user to be able to add just one of a specific product.

Essentially, it’s a free sample, so I don’t want the user to be able to add 50 or something like that. It still needs to be its own product, and not a free item that gets added to another product.

Any ideas???