There is no magic.....
Sellers try to get as much as they can..
Buyers try to get it for as little as possible...
Somewhere in the middle the 2 shall meet and both will be happy.....
If you don't know what to look for, bring someone who does, this you will only learn with time, no one can teach it too you on a forum.
Stick to your budget, if you don't you will potentially just be spending more and more.
Everybody thinks their shyte is worth gold the trick is to find the gold and leave the shyte behind...
I am not sure what else I could offer you, but once you find what you want, you will buy it...
good advice here. was about to say something very similar.
There is a variance in price because private sellers can post up whatever price they want. Some price it reasonably, some don't. Some post a bit of a higher asking price to leave room for negotiation, some people are firm and wont negotiate but they price fairly.
Here are a couple tips from me...
What to look for / things to ask:
How many owners? -The less owners the better in my books. A person who's owned their bike since new and for many years probably took care of it, vs. a bike that has exchanged many hands. personally I like buying bikes from the original owner, but these are hard to find on older bikes but if you have time to wait for the right one it'll come. Take this with a grain of salt though, there are still bikes that are original owner that have been poorly maintained, and bikes with multiple owners that have been very well maintained and cared for. But statistically id say the less owners the better.
As-is or with safety? Find out if the seller is willing to include safety. If not, ask what the bike needs for safety. It could be something as small as rear brake pads, or as big as 2 tires which can run you 350-450$ at a shop. items needed to pass a safety can add up costs to your purchase that you'll need to fork up after buying the bike. A bike thats ready for safety is the way to go. Otherwise make sure you include these items into your budget post purchase.
Tires / Brakes / Battery / Fluids (Oil, Brakes, Coolant) - Ask how old these items are, look for a bike with these items being recent / newer. Also shows the bike is well maintained.
Valve checks - ask if there is any service history on the valves. When they were last checked. This is also a big maintenance item to take into account.
Any accidents? - Avoid a bike thats been down at high speed. A bike thats been tipped over at a stand still is not that bad in my opinion depending on how bad the damage is. Its mostly just cosmetic damage as the bike was tipped over (2 of my bikes have tipped over at a stand still, and I have in the past purchased a bike that was dropped at a stand still once too.) Damage can be very minor and unnoticeable, or very bad as in cracked fairings, scuffed engine cases etc. If you look at a bike that has scrapes or rashes one the engine cases / side covers you know the bike has been down. Look for scuffs on "corners" of the bike like the corners of the front cowlings, bar ends, ends of the mirrors, foot begs, exhaust, sides of the fairings of course, etc. to know if the bike has been down. If there are signs of the bike being down and the owner says it hasent, be weary, as the seller may not be honest about other things.
Find a clean bike: I like buying bikes that look "clean" and as original as possible. If a bike has mismatched fairing colors, too many stickers or it, and silly things like that- be weary. Not saying these bikes are all bad, but it just makes me feel like the bike has been down possibly and has been put back together with random plastics, or that the bike hasn't been maintained well. At the same time, expect to see regular signs of usage from an older bike. These are fine. Minor scuffs, that you would only notice if you looked closely enough are ok in my books on an older bike. Know the difference between regular signs of use and real actual "damage". An older bike can be "mint" and "clean" yet still have minor cosmetic flaws. Know what these are. As long as the main parts of the bike are in tact and good condition, dont sweat the small stuff.
Price: Check what other bikes are going for, go see a couple. See more than one bike before deciding, so you have something to compare them to. unless you know what to look for and find the right bike at the right price- sometimes you need to pull the trigger quick as the next person that comes to see it may take it while you go home to think about it. Negotiate if you can. Sometimes a seller will go down $1000, another may only go down $250. Depends on how they priced the bike in comparison to others and the condition compared to others.
If a seller allows you to test ride the bike (some require cash in hand), go for it if you're experienced enough to take it out and see how it feels. Look for any abnormal noises, vibration, or bike not riding straight. Test all the gears, feel the clutch for strong engagement, test the brakes. Bike should run smooth and feel solid. If you don't have enough experience to test ride it, have a friend do it for you who can.
Good luck!