I had a similar experience. There is a small local bike shop I regularly went to, when I needed to order bits. The problem was, that the mechanic was a bit of an arris, even though he was quite good at his stuff.
I'd bought a few bikes from them and anytime I had a problem, they'd offer to give me a run home or give me a loan of a bike. We're not talking demonstrators here, it was just a small shop, so they'd give you a loan of one of the bikes, which they thought, you'd be interested in buying.
I got on quite well with them until I bought a chain & sprocket kit. I did a search around the web and managed to pick up an AFAM chain & sprocket kit at a very good price. I changed the sprockets myself and then asked them to swop the chain for me. The mechanic was acting like a bit of a plonker and making it obvious, that I should have bought the kit from them and saying it was probably crap and wouldn't last very long. When I got home, the chain was solid, I had to loosen it off myself, which I shouldn't be doing, when I've just paid somebody to swap ot over for me.
There's another small mechanic in town, from now on if I need anything mechanical done (which I can't handle myself) I'll go to him. I haven't been back in 6 months, its their loss, not mine. All because the mechanic is a tosser. :verysad: