Condition is all important as they don't hold up well to not being regularly cleaned/polished. They also don't like not being run on a regular basis. Leave them parked up for a month and they can struggle to start and on that note
never try starting one with a weak battery as it will eat the starter spragg and cost mucho £'s to sort out
Rev counters can become erratic and fail also check how many gears it has in the box. Five is standard (unless it's a TBS) but some owners fitted a 6th
Paint is normally good but chroming can be a bit iffy. The plain alloy motors with polished alloy casings always look smart and getting one with as many genuine Triumph accessories on it is wise as even if you don't like them there is a big market in 2nd hand parts and they do fetch big bucks . I've seen chromed radiator end caps make £200 whereas the original black ones can trade at around £25
Look after it and it'll bring you many happy miles and much joy in ownership whilst going up in value. Ignore it and it can end up being a money pit