by -Adam- » Mon Nov 30, 2009 1:07 pm
Sounds more like the derailleur was not properly adjusted, either way, school boy errors. I would go back to the shop and get them to sort it all out, free of charge of course. If they won't, find out if he's qualified and speak to the body who certifed him!
Better yet, learn how to do it yourself. Chains, derailleurs, cables, take no time at all to adjust properly.