man honestly, try stuff before you buy it and see what yo uthink. You could buy an amp off the internet and have it turn out completely different than what you thought, OR you could find something in a shop that sings to you.
Trying is surefire insurance that you'll know (and hopefully like) whats comin out. See, that was my problem, i got a 6100lm off webay andd was like "why the hell did i buy this" for the first number of months... until i picked up an od808 and a nicer guitar with nicer pickups.
But still, that first initial regret can be agonizing. Thank god my expectations were low after my previous line6 spider II.