I am working on a couple of (actually 3, now) salvaged/purchased bikes and would like to tell about what I found.
Bike #1 was a GT Windstream comfort bike. I assume it was a bike store bike.
Bike #2 was a Religh M20 ladies MTB. I assume it was a bike store bike.
Bike #3 was a Magna Glacier Point MTB. I assume it was a dept store bike.
Both the #1 and #2 had Shimano crankset with integrated 3 speed chain rings. By integrated I mean they were a single unit of spot welded chain rings, connected to the center of the right hand crank arm in a somewhat rivet rike fashion (multi toothed). The disadvantage of this system is that it does not have the 5 armed spider that one finds on brand name crank sets that affords interchangeability of chain rings. Also, in both cases (#1 and #2) the bikes did not appear to be used much, but the chainrings were missing several teeth. The material of the rings is apparently just plain stamped mild steel.
Now, bike #3 had a one piece American style crank arm and a 2 chain ring unit which is riveted together. Also, the one piece crank connects the chain ring unit in the usual place which is at one pint away from the center. I think this provides more leverage than the center driven mechanism in #1 and #2. The chain rings are also made of better material and are in much better shape, quite reusable. Other parts on this bike were of much inferior quality, e.g. the shifters were plastic and caliper brakes were stamped steel. But the bike probably cost 3 times less than #1 or #2.
So, my observation is that one needs be aware of the fact that LBS bikes also have low quality components, especially the crank set with non replaceable chain rings. When one ventures to buy a low end bike at a bike shop, one needs to make sure that the chain rings are attached to the crank arm by a spider and a set of bolts to insure that one gets good quality chain rings.
I also looked a magnified picture of a Trek 7.2FX bike, as it was advt on CL here, and found the same offending crank set on a bike that would cost $350+ in a LBS. I think Shimano should be asahmed of producing this crap. I would prefer a no name one piece crank to their so called SIS crank set, with a plastic chain guard ring hiding the poor quality chain rings.