He sounds like he's not BS-ing you. According to Motor Magazines a/c article, 4/04:
"Todays condensors have such small flow paths they're virtual traps for a lot of debris. You need only replace a restricted condensor to restore a/c performance, not return a replacement compressor that isn't the problem. Furthermore most aftermarket a/c specialists have learned to protect themselves, typically by flushing where appropriate and installing suction side screens at the compressor inlet and liquid line filters".
It might cost you more initially but you are getting steps that should make for a good a/c performance and a through job.
