Why not introduce yourself in new members?
The R125 is very popular. Yamaha took styling queues from it's sports bike range for the design of the bodywork. They have also updated it at reasonable intervals, avoiding it becoming staid like the CBR125.
As with any bike you view check the VIN plate has not been tampered with. Check for crash damage [imo minor marks are normal] but things replaced with gleaming new parts should set alarm bells ringing. Always ask if it has been dropped. And qualify this with 'at what speed?'. Also HPI it. Some kids buy them on finance and then discover their apprenticeship wont cover the payments and try to sell them on. You'll be lumbered with the finance if you buy it. Some people may also put damaged repaired bikes back on the road [nothing wrong with this if done with scruples] with out declaring to potential buyers the previous 'write off'.
The earlier ones were a bit fragile reliability wise, not helped by attempts to tune. Anything after 2012 should be better, but make sure it's had regular oil changes, has been cleaned and check wheel bearings, if it has done more than 12k miles. Avoid anything with modifications, they may be tempting but if not done correctly they may shorten the life of components.
I'd get an insurance quote to. These R125s, due to their popularity with idiots and thiefs is quite a lot more than some other 125s.
I like that they have brought new blood to motorcycling, i dislike the new price, it's obscene.
Edit: also notice at the bottom of the ad, there are links to the MT125. Look at those too.