Is this guy on Craigslist full of B.S.?

I'm late to this party but here's my take based on your initial post:

He has a Prolong charger/discharger system he bought for $700. He buys battery packs out of salvage cars and recovers batteries on trade in from cars he replaces batteries in. Do a Prolong maintenance on the pack and it's balanced. "Matched" can very easily be they are original with matching serial numbers or they're matched because they've been balanced, matched as best they could be to the rest of the pack without actually taking the time to deal with it properly..

Estimating you'll get 15k miles out of his packs is easy when he doesn't offer any warranty or he's a guy who can easily disappear from the marketplace when the complaints start pouring in.. 15k is only one year for the average car these days. After a thorough, full Prolong session just about every battery will probably get at least 6 months and could very well last a year.

Absolutely no way I'd do business with him. Sounds like someone trying to prey on the unsuspecting.