Anyone that has a boost controller with no boost guage is an assclown. Run far, run fast. Plenty of other cars out there. Or, you can buy a guage and just run the line through the window. Have him get on it and see what it is. If its a reasonable boost setting, go for it if you trust his other work. If its set to 20 psi, you may want to pass.
The t25 on a 2g cant do a whole lot of damage so you may opt to buy the car anyway. A 1g with 14b though could have some damage. Do a compression test at the least before you buy it.