I am not a lawyer, but I ran into this once. In the US, the Uniform Commercial Code exists for this very reason. It works well and you are protected when you buy a stick of gum at the store. No receipt and you take ownership of the gum when the Seller accepts the money. The owner can not ask for it back. As for the DR goes, I have no idea. But you clearly go to the Colamdo and fork over 50 pesos for a fria. Once you take position of the beer, I doubt you would have to give it back if they changed their mind and wanted to sell it to someone else. The more expensive the item, probably the more complicated the issue. So it depends on what you are talking about.