"High mileage" is both a subjective and objective term. I've been writing a used ebike buyer's guide - here's an adapted excerpt:
I've gone through dozens of ebikes and put tens of thousands of miles on them in the past 6 years, and bought/sold a few used ones along the way (I haven't had to "junk" one yet, knock wood). In my experience, lots of rides adding up to 750 miles in a year is kind of a good thing because that means the battery probably didn't sit idle for long periods.
This is especially true when people charge their batteries to 100% after every ride because lithium cells don't like to be kept at a full charge for extended periods. That practice can diminish the battery's capacity and/or lifespan substantially, even in just a year.
It can also be detrimental to keep it at low states of charge, which can lead to "bricking" the battery. Ideally, the seller kept the charge level between 40 and 80% in a climate-controlled environment when he wasn't riding for days or weeks on end - another battery storage no-no is extreme temperatures.
Some ebike-specific questions you might want to ask the seller:
- Where was the bike kept?
- Was the battery stored separately, and if so, where? (If in a garage, was it climate controlled? If a basement, was it dehumidified in Summer?)
- What state of charge was the battery kept between rides?
- How long were your rides, on average?
- How long between rides?
Regular bike stuff - brake pads, chains and such - is generally inexpensive to replace on lower-end models, so it shouldn't matter much if he rarely or never cleaned or lubed his Himiway's chain, replaced its brake pads etc. Just be sure you have a trusted mechanic handy if you don't do that kind of work yourself.
I'd also take it for at least a 10 minute ride to make sure it's comfortable for you and everything performs as it should. In all likelihood, a 1-year-old bike that was stored inside should be okay at 750 miles, but look closely at the frame, fork and wheel rims for dents or bending, and listen for any clicking, grinding, or creaking noises. Potential sources for those are too numerous to list, but some could be very costly in short order.
If you decide you want to buy it, make sure you get the keys and charger
Hope this helps - good luck!