"¿Estás interesado en comprar ...?" "¿Quieres comprar...?" "¿Te interesaría comprar..?" "¿te gustaría comprar...?" There are many options to say that. use the one you like best good luck ^^

I'm completely agreed with previous suggestions, but in formal situations as commercial meetings it'd better use "Está interesado en comprar..." or "Están interesados en comprar..." using the third form of singular or plural instead second ones.