They should be good as new. They are an authorized repair shop. They use authorized replacement parts. The amps are good as new. Just may have scratches etc. And they receive a warranty iirc. If there was an issue with a repair it usually rears is black head very fast
If used properly a good quality amp will last years. I wouldn't think it would be unreasonable to expect one of these sundown refurbs to last a good 5 years or more.