(Rampant cross-posting snipped)
Hmm. Wasn't that 20 years of experience, just yesterday?
Take a look at uk.rec.cars.imports for the past few years (no idea how popular this group still is) for tips. Also, like everyone else on the web, take a look at rival sites.
You'll also want to compare prices and specifications - I'm guessing that you're transporting or driving the cars across the border from down south?
Well, Irish cars generally have a very different specification to UK standard. Personally, I'd be unlikely to buy a car with an inferior specification (harder to resell) or anything pre-registered with an NI plate (not sure of the procedure, but wouldn't I have to pay to get it reregistered with a standard UK plate? Or has that all changed with the new system?)
HTH
Hairy One Kenobi
Disclaimer: the opinions expressed in this opinion do not necessarily reflect the opinions of the highly-opinionated person expressing the opinion in the first place. So there!