As long as the service history is in check it shouldn't be a problem. If it doesn't have full history (i.e. stamped book) check for receipts and dates. Be clever as well, if he has a receipt for an oil filter that was say purchased a couple of months a go, have a look at the filter and see what state it is in as well to see if it all adds up. Could also check the oil to see what state that is in.
I'm not sure what the service intervals are on street triples, but make sure the owner isn't trying to shift it before a major service (valve clearance etc).
I wouldn't let that mileage put me off, just means it has been used and not sat in a garage.