I think you answered your own question in the title.
I have access to unlimited checks and I perform quite a few, on old to new cars. Its safe to say I've never seen one with a credit discrepancy, about 1 in 10 I check has a changed numberplate (legitimately) and thats about it.
I'm gonna go on a limb here and say that the power of these things and the associated risks of not using one are somewhat exaggerated by, yes, the people who try to sell you one at £35.