If it was taken care of (you can usually tell just by looking at it) If it shows less than normal wear for it's mileage, and is clean. then it is probably ok. About the only thing scooters need in the way of maintenance that a motorcycle doesn't is the belt and possibly the rollers replaced once in a while. Neither is expensive, unless you have it done by a dealer. A dealer will charge you $50 labor to add air to the tires. Most have a 1/2 hour minimum on labor, and dealer labor rates run around $100 an hour.
I have 17,000 miles on an '08 Vino 125, almost all of it at wide open throttle. The belt has been replaced once (by me), other than that, just routine maintenance, though I do tend to over maintain it. I change the oil about every 1000 miles, and am on my third rear tire, second front tire. I'm also on the heavy side at 220. I fully expect this scooter to last 50,000 miles. Valve adjustment is super easy. But do some research on that for the scooter you are considering. I was about to buy a new PCX150, till I discovered it takes over 3 hours just to remove and replace bodywork to get to the valves. I now plan on a Zuma 125. ( I don't really need it right now, but a dealer made me a ridiculous trade in offer on a crotch rocket I want to get rid of, so I decided to just trade and not have to deal with Craigslist) I plan on riding scooters the rest of my life, and just keeping one motorcycle, a cruiser.
I won't spend more on a bike than I think it's worth, but if it's a good deal, I don't seem to have a problem buying bikes I don't need.
2002 Vulcan 750, 2013 Royal Enfield B5
2001 XT225, 2009 Genuine Stella
1980 Puch moped