many atime i've been in mountain bike shops and at one shop they were okay if i popped behind the counter into the bay to help them out whilst i was chatting to them. they had to stop me doing unauthorised work on bikes when i was really bored though. free servicing on bikes wasn't going to do them much good, lol!
i remember one shop was doing the maintenance for the ambulance cycle crew here (we are the country, possibly even europes leader in emergency cycle teams (police/paramedics) in my home city, anyways, this paramedic had gone for a single ring up front rather than 3 rings and shifting issues, but the shop had spaced the chain device wrong and i used the same chain device and had fitted it to 3 different types of awkkward frames, so i offered to go behind and do the work and they wouldn't let me! instead putting him back to 3 rings, shame really, i thought this case was special, after all we cant have the emergency service crippled due to inexperienced technicians (not inadequate, just inexperienced with the specialised gear )
the only reason i didn't bother trying to find employment in a bike shop was i wasn't going to clean dog poo off other peoples bikes or fix their punctures when they should do it yourself. theres nothing more soul destroying than a father taking his son out for the day to a bike shop to fix the kids puncture!!!!