Back in the day I would agree...
Now I think, first of all inspect or get someone to inspect, to identify any rusty components first and then decide what to do with them, before... covering them up, as it were.
I had the local change independent change my bulbs.
They weren't brighter as such, but newer, which... made them brighter.
And I use this stuff for headlights. Cheap, needs to be repeated every so often, but works well...
I would be thinking, the usual due diligence, MOT check, HPI check etc.
Also a search on this forum will turn up lots of useful info., e.g., "RX450H buying ".
And I'd be thinking, who am I buying from: private, dealer, Lexus dealer...