Went and looked at the bike last night. Seller was a jerk so we walked away.
What part of, please do not start the bike before we get there and let us see it start cold is hard to understand? Engine was so warm you couldn't touch it bare handed. And he lied about it. So no point in even looking at the bike.
Probably a smart decision. I've had the F800ST as a loaner, but we lived with an '11 F650GS twin for 110k miles or so. Same engine in both, as Squibb noted. The early years of that 800 motor had a tendency to burn out the stator around 40-50k miles. They upgraded it in '15, IIRC and finally let you order just a stator instead of a stator and flywheel package, which was around $1k when ours burned out.
The cooling systems are really marginal for that engine. The coolant reservoir cap just has a small hole in it, no overflow hose. So when the bike gets too hot, it sprays hot coolant out of that small hole. On the GS, that meant strait up in the air and back on the rider. Messy and not pleasant. Ours did not like triple digit riding. We lived in the desert too, (St Geroge, UT, service in Vegas).
With any BMW, it's important to be aware of where your nearest dealer is. Other shops won't work on it, and you need someone familiar with the BMW stupidity in terms of design and requirements for service.
Some bikes are better than others. Ours was a lemon and after the engine burned up and they built a new one from bare cases for us, under aftermarket warranty, it was much, much better.
Your neighbor might find bikes like the Yamaha FZ6/FZ1, MT series of naked standards or the Suzuki Bandits appealing. If he has a budget, get him to do some searches on cycle trader, with just price as a search and see what he finds interesting. Good of you to help him out.