I have bought my last two cars from an auction. As far as the advice about someone knowing about motors is concerned, its not that cut and dried.
I’ve been a mechanic for 30 years and there’s not much chance to check them over as they only get opened up and started when going into the selling area.
Basically it it looks clean and tidy, has a reasonable mileage, and some form of service history, then its up to you to set a price limit and take a chance. Listen very carefully to the auctioneer about sold as seen, warranty, history etc.
My last car cost 3.5k and the clutch was stuffed (£350 for a duel mass flywheel) So its up to you to take the chance if you think theirs a bargain to be had.