it's an utter nonsense that there's zero service records .... unless the previous owner has died or gone gaga and all the paperwork is lost ( thrown out by executors ) then it is inconceivable that the owner didn't keep his records .... it's what one just does, especially when " looking after " a car and doing 3/4000 miles a year.
I wouldn't believe the dealer, especially offering a filthy car for sale too
However, all is not lost ............ a brand new MOT from YOUR service guy/MOT station before you buy it and at the dealer's expense and a full service after, addressing all and any issues, then maybe you should think about having it ...... at an acceptable price.
Malc