Depends on how much it's worth. A couple of grand, then no point asking, as someone will always buy it back, but still get it HPI checked. If it's worth £10k, then yes, get it checked over so you avoid losing a lot of money.
The best route for genuine peace of mind is to use an acredited vehicle inspection company. They start with an HPI check, and then give it a full mechanical check and road test. This will highlight any problems, and can either give you a chance to walk away, or a good bargaining tool when buying. Yes, it'll cost you a couple of hundred quid, but at least you'll know...