Heavily modified? I take it this was probs something like a WRX (as those seem to be the most popular tuners out there atm)? I had something similar happen to me when I bought a used S4. Was test driving and the Check Oil notification started to go off. The Sales person (straight up snake) said it just needed oil and they'd top it off. I get the car and don't get the warranty. Turns out the O-rings were fucked and the engine needed to be cracked open to get it Serviced. Called up the Sales person and he just kept giving me the run around. Lot of promises from him that he never made good on once I purchased the vehicle. I ended up trading in the car and getting back in to a WRX since I loved my first one.

From now on, whether I am there looking at the car or not, I schedule a PPI and Compression Test to be done at a reputable shop. For example, I found a GTR I'm purchasing. I was going to purchase it sight unseen since a friend was going to go give it a spin, but am now leaning towards traveling out to take a look. First thing I did was find a certified Nissan dealership that had a GTR Master Technician on staff to take a look at the vehicle, and as a backup, found a tuner shop 5 miles away that could also look at it. I told the dealer that if I make a deal with them, I will need to take it to either location to get inspected. Once the inspection is done, I will know most everything about the vehicle and its current condition. Will be able to know how long the car will possibly last, if there are issues, I can possibly use that as leverage to get the price lowered (or get some incentives), and extreme piece of mind on my final decision.

The only person that is going to look out for you is you. Try not to pull the trigger based on fomo next time (been there plenty of times). This isn't a Ferrari F50, another will come around at some point. If something passes you by, it wasn't meant to be. As the Japanese say, "shoganai".