I am apparently in the minority, but I love Gerber flats. I used them all the time on DD1. I doubled them up, folded them in half the short way, then bikini twisted. Now I have a full stash of pfs for DD2, so the Gerber flats pretty much get used as burp cloths. They've been washed so much that they're crazy soft and way past pilling. I think the pilling disappeared after the first week or two.
But I have to say, I totally don't understand why people buy or sell used flats. LO isn't big enough for my GMD larges, but I still use them all the time for carpet spills, burp rags, changing pads, drool bibs, floor coverings for tummy time, and the list goes on. There are always a few floating around each level of my house. The more they get used and washed, the softer they get. And the cost of shipping them is close to the cost of buying them at retail, so I can't for the life of me see why it would be worth the effort.
Rebecca, married to J (2007), DD1 Anna (11/09) and DD2 Ada born at home 7/12 DS Henry born at home 3/14