I am really mechanically inclined.
Ok so, one thing I have found helpful is to take a look at the ads and keep looking...
Get a feel for prices that way, search also for completed sales / sold listings.
I would do that for some time, until you get a good idea...
Also you need the money, all of it.
Because if you find a good deal you're not going to want to try and haggle with the person selling it... Seriously, we're looking for deals and deals only. Everything else is a pass.
No bargaining at the point of sale, do all that before heading out, get it out of the way before wasting a trip.
Once I get in my vehicle to head out, I am 90% sure I'm buying what it is, for how much they asking or what we already agreed on.
The only way I won't buy it is if something serious comes up that I didn't see in the ad (whether it was there or not), the machine isn't what I was looking for, it's not what was in the pictures, or "we sold that one but here's another"
Last but not least you need something to transport it back with.
If you show up at my house in a Honda Civic and I'm selling a Dixie Chopper the first thing I'm going to ask is how you plan on getting it home? Because if you have no way of getting it home ...
So, have a trailer and make sure it's wide and big enough, this also needs to happen before even responding to the ad.