Second, make some observations. Third, find out the gallery's policies. It's the last free credit in America. . . . Yes, they exist, but retail prices do not assume discounts in most galleries. The best approach is to develop a working relationship with the dealer and to politely inquire as to their view.
Art is a personal decision.
A quality gallery will often accept the prompt return of a piece that just didn't work once you got it home. As in all transactions with real human beings, reputable dealers will do their best to negotiate with you in all of the above scenarios to reach a mutually acceptable solution. You can't read Consumer Reports to determine what painting you should buy. Consequently, the relation between a gallery staff member and a customer is quite different than the typical sales experience. Your first view of a gallery may be surprising.