I had a bike built for me by an LBS (Surly Pacer, SRAM Rival) in July.

I'd had trouble shifting up to the large ring for some time. After multiple trips back to the LBS owner who built the bike, it was finally tuned correctly by a different LBS (actually a local franchisee of a national chain).

Anyway, the original builder said I had worn out the chain (less than 3 months, 700 miles, no cross-chaining). How? "You must be a pedal masher," he said.

This sounds like BS. 700 miles on a chain? (SRAM 1031). The second LBS who fixed the shifting problem noted that the b-screw adjustment was way off on the rear derailleur. SRAM states the upper wheel of the rear derailleur's tension pulley should be 3 or 4 mm from the largest gear. Mine was like 4 inches.

So, presumably this put more tension on the chain. I noticed when I sat on the bike (before the fix) the chain had no wiggle -like it was going to snap. Now I can reach down and nudge it a cm or so with my 210 lbs self on the bike. There's less "binding" noise now too while riding. Could the b-screw be what caused the chain to last only 700 miles?