But how do you plan to do it? If what you think is that someone is going to buy the items before you send them the Bitcoin, I don't think anyone is going to do it. And I wouldn't recommend doing it the other way around either.
maybe he'll agree to send bitcoin in advance. I have not seen that it is not an option.
OP, you definitely need to be a little more precise.
are you ready to send bitcoin first? (because of your rank here, it is mandatory)
what the value is of these items?
How much exactly is your "bonus"?
and whether it is a digital good or a physical one, and if they do not accept your country, do they deliver to your country?