This is an extremely important message. Fraud is very easily the thing that can sink many small companies that aren't used to the levels of fraud that you will see on the Internet. And because there are so many ways to defraud a merchant that isn't obvious, merchants need to be extremely careful and educated on the process. And handling chargebacks will become a full-time job for someone in your company, once your company becomes big enough. I work at a payments company, and fraud is something that ends up being a headache, although we are at lower-than average industry norms.

It seems relatively easy for someone to turn credit card payments directly into cash, by making a trade and then extracting cash through the bank account. And the gap between your withdrawal policies and the chargeback policies of credit cards are pretty wide. I would be very careful about this. Forcing users to enter bank accounts make it a bit harder for average people to defraud, but not a motivated fraudster. Also, allowing people to take delivery of wine through the purchase of a credit card, and then being subject to a chargeback will be extremely painful, although I'm not sure how easily chargebacks are fought in Europe. If you do suffer a lot of chargebacks though, even if you successfully fight them all, be prepared to be dropped by your credit card processor.

I think your business is actually very interesting, but I'm surprised that credit card companies would allow you to accept credit cards at all, since I would think they would lazily lump you in as a form of brokerage site. Not that I believe this, but it seems like an easy translation to stock brokerages, which don't accept credit card payments, but force you to transfer real cash into your accounts before you trade. Then once you have money in a brokerage, they can extend margin, but they maintain their own risk by monitoring the margin levels, etc.

Good luck though, I read through your site and I think it's a very neat idea!