As mentioned - know the sellers or auction house conducting the sale.
Knowing either will give you a good idea of the quality of their wares. Good auctioneers dont sell to poor quality sellers - they have their regulars and wont risk chasing them off for 10% of a low grade sale 1 time.
Amish co-ops regularly hold auctions, it eliminates any "haggling", allows everyone to get the same market driven rate and attracts more buyers to a highly fragmented seller group (could you imagine being a buyer and trying to contact 50+ amish families, much less 500 that some higher population area attract).