yes its possible, weather or not its legit is another question.
we cant veiw the car for you, go have a look see if its in good condition, see what mods has been done, see if you like it take it on a test drive, if your really botherd about how much power it is ask the guy whos selling it if he has the rolling road print outs, if not see if rtech have any.
rtech did loads of people on heres maps and used to be a forum sposor so there good guys and know what there doing. i wouldn't be botherd about the map/power claim ide just treat it as a normal car, look it over make sure everythings ok have a drive, if you like it go for it if not then dont. then if you want more power look into getting a stage 2 map or doing other mods.
either way a mk4 with 80k in good condition usually sells for around 1k-1.5k