Getting a good amp for your speakers...is like to be chicken in Kentucky...hard job. This is the reason why all the last years I try to listen many components as much is possible. Ear education and familiarisation with different stuff is a good habit. Culture help in forming the personal taste. Even the reviews and the net culture could reveal the best matches betwen components. About buiyng: Yes, a stunning good sound of a particular piece in showroom could not sound the same at home because the dealer reveal a piece just after many trials and after he find the perfect synergy between the others components. Usually you don't have the same components at home so you'll have a different sound.
First law is borow and listen at home because this is the best evidence for your ears. Even a dealer (who now the best how things work) must have no problem with this as much you grant with the value of the item. The filosofy "listen here and buy or not" is a bad idea for any hi-end dealer. In this domain everybody must provide understanding and trust. We talk about expensive purchase for long terms. Even more if the seller is private and the item is used. Be aware to any sugested problem in a previous listen proposal, don't go further. When listen, don't rush in a hurry decision, the amp need to break-in and yours ears too. In some circumstances different not mean worst.
Finnaly, a good amp is not necessarly to reveal micronic details or blowyng socks bass, the most important is how happy are your ears with the music provided.
But perhaps you know already all this. I hope to find the best amp for the speakers, try-it first if is possible.
Good luck!