Don't do it.
I spent DECADES going through crappy mower after crappy mower.
Last year, I finally bought a new Husqvarna. I am NEVER, NEVER, NEVER looking back.
New riding mowers start at around $900. For your $900, you can have a nearly unending supply of aggravating headaches, along with a plethora of pains in the arse, and every other place possible. You can also have your lawn nearly never finished, because of breakdowns.
After 2 years of aggravation, you can sell it for about $250 and start the joy all over.
A used one has the same issues, plus low compression, bad batteries, half the lifespan, and zero resale value.
Buy a name brand. In my area, that means Husqvarna or John Deere. Buy what other people want to buy.
I paid $1600 for mine. I will easily get 4 or 5 years of good life out of it, and then be able to sell it for $1000. That's pretty good math.
Starts every time, works perfectly. I bought the hydrostatic transmission not because I cared, but because I know buyers want it. My wife and 13 year old d most of the lawn care, and never call me for help fixing the darned thing any more.
One buying tip- unless you live on the 16th green, most normal people's lawns are no where near as flat as they look. Holes, roots, etc are really rough on steering linkages. If you put a little weight over the front wheels and try turning the wheel, it shouldn't feel like you are bending, straining, or about to break something. Cheap mowers will feel like the steering linkage is about to snap. It is.