Pull back carpets in boot and around rear lights and check for panels that have been repaired, from low rpm in 4th go full throttle and listen for a whistle ( will get woosh noise from turbo this is normal ) that would indicate DV valve.
Look for signs of arch rust, panel gaps, headlight and bumper/bonnet alignment. View the car indoors in the dry. Look for signs of paintwork by looking for any overspray and/or traces of white powder in door rubbers and door shuts from polishing.
Ask to see the logbook, get the name and address of previous owner from it and contact them, ask about the cars history.