Personally, i'd go new if you can. What are you going to use it for? If it's just for 4wding (as in, all short-ranged stuff), then a new hand-held might be a good option? The hard-wired units are fantastic, but are more expensive to install and repair, and unless you're doing long-distance convoys, or longer range comms work, can be overkill.
Having said that, i've got a second hand Tait UHF, ex-ambo radio, and haven't had any problems so far.