The programme is a total sham and would only ever impress kids who know nowt about what they're pretending to do.
Caught a bit of that MGB they were doing and they bought a pair of good condition matching chrome bumpers for £30 and a pair of chrome bullet mirror for £3 from an MGB used parts specialist - absolute fantasy that you could purchase kit like that for the prices they supposedly pay . . embarrassingly unrealistic.
As for preparing car body's for bare metal respray by grinding them all over with angle grinders - well I'm not saying it couldn't be done but it would only ever be done by a cowboy - any professional would simply get the shell blasted (sand or more often baking soda nowadays) because grinders could only ever cause damage to the good metal and leave flat runs that would need taking out.
Funniest of all is that their cost figures are skewed because they don't include for overheads (premises costs, depreciation, business rates, wages, taxation etc.) and the posing wanker who values the vehicles doesn't even examine them . . in the real world the fact is that they would lose money hand over fist.