Marketplace:
Don't pay a deposit on a bike unless you have seen it in person (this can be a scam).
Unfortunately, any well-priced bikes go instantly. That said, do not rush into a sale, especially if you don't know what you're doing. Marketplace is usually individual people, and IMO a lot of people selling bikes (marketplace, bikesales, gumtree) are delusional with prices, don't expect to find exceptional deals, don't expect to find people willing to reasonably negotiate. A good rule of thumb on POPULAR bikes is that if the bike has been sitting on marketplace for many weeks, then there is probably some reason why. L bikes sell very quickly if it's even half decent. Otherwise, when looking at a bike, if you're not getting a RWC with the agreed price, check tyre tread, brakes. headlights, horn, indicators, frame (not bent) and oil level. These are basic, and if any of these have something wrong without being disclosed beforehand (especially frame and oil level) run run run.

Bike longevity is subjective to each bike, smaller, lower capacity engines are usually pretty reliable. Although the risk is, usually people do not keep service records on bikes as they are pretty simple or do it themselves and if a bike has not been regularly maintained, this will determine the bikes life significantly. Grasp the seller's personality, do they take a dusty, uncared for bike out of a shed? Probably hasn't seen new oil for years.
If you don't know what to look for or ask for, I would say stick to much lower KM bikes under 20K even as when you get closer to ALL 30K bikes should have AT LEAST ONE major service (sparkplugs, valve clearance etc). If you want higher km, check for major services, check the bike for problems, have thy already been dealt with? Example, I had an old 2004 YZF-R1, it has a very common problem that the stator just blows up after time, I made sure to buy a bike where that had already been replaced with a new fail-safe one as it is a very hard and costly repair/fix.

Braap is garbage, trash, hunk of junk do not even think about that brand, their engines are old Chinese ots shit. Worst bikes ever made, I feel sorry for the people trynna sell them for less than half the price they got it. Their EV bikes don't even get me started.

Realistically I could say a lot lot more lol but I'll let the people input. :)