Welcome, You will have to make up your own mind, ask for the details of the modifications and the companies that provided or installed them, search the internet for the companies and any reviews of the equipment/installers, check the modification section on this forum for the items that have been fitted chances are someone has fitted the same.  Finally have good look round the car for any signs of neglect, as an example I bought my first Abarth used from a dealer I never noticed 2 new front tyres at 6000 miles on clock (thrashed) and lots of little nicks and scuffs on bodywork only apparent when I cleaned it for the first time.

Beware insurance implications check quotes from club insurance providers on this forum.