Looks nice, but he is asking show car restoration price. The TR4's have really been going up in price, but for what he is asking it should show and drive as new.
The engines and transmissions are quite stout in these cars. Rust is the big deal killer. While it is a frame on car build, the body is also partially a support member. Look everywhere for signs of rust. Sills, frame mounts, etc. Look for even gaps around the doors.
Unless you have driven old British sports cars, you may be in for a disappointment. The are slow, noisy and built with the same quality they built tractors. But if you accept their limitations, they can be great cars.
Unless it looks like this car, I would not be paying $23K:
Triumph Other Convertible | eBay