We are talking used cars with a value of ￡2.5K+ where the mileage and records may be more important (It’s regular to use odometer correction tool to do Mileage correction), and in no particular order.
If you’re buying privately make sure that not dealing with an undercover small dealer, many such sales go hand in hand with clocking. Same goes for the V5 not being available or in a different name to the seller. There is no excuse for this.
Never buy without a documented and complete service history. This can be receipts, a stamped service book or a lease printout sheet. HJ likes receipts rather than/as well as a service book but I’m happy with just the book.
Open the service book and see they relate to the vehicle concerned. Look to see that the mileage patterns over the years fit in with the claimed usage. For examples fleets don’t buy diesel Vectras to do 7K a year, more like 45K+. Chat to the seller and note if he commutes 80 miles daily yet his yearly mileage is only 10K. Then something is up.
Most important is the “feel” of the vehicle. If you work on them you know what to expect at various mileages. Even the look of an under bonnet area can be a clue.
Private owners and fleets that might clock between services could be hard to spot. But they still have the odd item that strikes as odd, like the make and condition of types being wrong for the displayed mileage.
Owner craftily clocking car between services but realizes at a genuine 50K he is risking timing belt failure so asks for it to be done “early” by the dealer. Dealer puts it on the invoice or marks up the service book. You would have to think really hard why any owner would change the timing belt at an indicated 25K.
Also if you ever look at a car and find a little bit of card in the coin tray/change recess that is marked with the speeds in 3rd/4th/5th at certain revs wonder what that is for!
Sometimes “next service” stickers are left in after clocking giving a glaring clue as to the history.
There are a load more things but they are small items that you note in a fleeting moment that then build up a picture over 10mins or so walking round and chatting to the seller.
Overall it is about knowing what the likely mileage is of the car you are looking at and then asking very hard questions about any deviation.