Pull the hoods up and there should be a part number embossed on the plastic body somewhere. ST-Rnnnn or something similar. Knowing that you can look at the release dates to guess what age the components might be. PN will also be on the back of the parallelogram of the RD. That'll tell you what it is so you can make sure it'll handle any gearing change that you might want to make to the rear cassette. As well ensure the guy that built it out didn't go outside spec and is selling it because it never performed well for him.

Since it appears that you are local to the bike, you should ask for the saddle to be set to the correct height for you. Then judge what the saddle to bar drop is. If you need higher bars than what it is on that bike, then you are looking at the wrong bike. You can get a ballpark for the saddle height by putting your heel on the pedal and extending your leg almost straight.