I've done just fine checking barrels by holding them up to a light source in the gun shop; look from the action, swap it around and look from the muzzle. I've never needed a bore light to do this job and never been disappointed with the bore when I got them home.
Crown is important but not the end of the world, more important is to check the throat for erosion or wear. You can do this observation just by eye, using the method suggested above. Look at the condition of the rifling in the first couple of inches of the bore from the chamber and compare then to the rifling elsewhere. You want to see a nice round leade ... if the throat is egg shaped or out of round, that's a deal breaker.
Don't be fooled by cosmetic condition, I've picked up some sensational rifles that looked beat to hell and transformed them in 24 hours. As long as the bore is in good shape and the action has a good positive lock up - nice and tight et al - the cosmetics can be improved at home. You can always use poor cosmetic shape as a bargaining chip as well.
A dark bore can clean up also ... as long as there is plenty of meat on the lands, it's a shooter.