not everyone are mechanics
Very true.
You'd
expect people to identify a bald tyre, but as has been said, there can be bulges, splits, cuts etc (not to mention cracked alloys) on the inner sidewall that unless the presenter actually jacks the car up or takes the wheels off to inspect the tyre, then they won't see the problems, and even if they did see faults, they may not know what they're looking at.
You only have to look at some of the threads of members here asking questions about damaged tyres.
I've carried out 10's of thousands of MOT's over the course of nearly 20 years, and nothing shocks me anymore with state of some of the cars presented (and almost all of those MOT's i've done at main dealers).
People really do think an MOT is a saftey guarantee for 12 months, whereas nothing could be further from the truth.
As for dodgy MOT's, it's rife, very very rife, and always has been.
DVSA have cut back and cut back on staff, and although their inspectors will visit all testing stations to carry out an audit, it can be once very 3 years if the testing station is Green on the RAG scale.
Hell, i could sit here at home, log in, wait 30 minutes then issue a certificate for any car and probably get away with it (i obviously wouldn't, as it's dumb beyond belief).
As for the OP's idea..
Utterly ridiculous!