Personally I think a used 300 is a bad idea for many reasons.
Think of the reasons a person is selling it so soon.
If it's because they want to upgrade, that means they have wound the heck out of it and still weren't satisfied. A person who is not satisfied with something is less likely to put that TLC into it to make it worthwhile. Especially n00bs and young guys.
I find it next to impossible that somebody would have enough interest in motorcycling to buy a brand new bike, then decide they don't like it. Especially not on this bike.
The last reason for somebody to sell so quick is because they crashed it. I'm a guy that if I crash it, I want a new one, it's not the same to me. I hate buying anything used because I feel like I'm buying someone else's problems. If I can't buy it new or with 100% certainty or trust that previous owner took care of it like I would, then I won't buy used, I'll just do without.
For the price, I can't speak for anybody's finances, but anything you can afford to buy used could be used as a down payment to get a monthly rate under $100 per month. Most cell phone plans are more than that these days and we don't even talk that much.
IMO it's too risky and not worth it to buy a used 300.
There's a remote chance you find that rich guy who likes to have a bunch of "toys" who bought it just because it was the greatest and latest. Maybe he rode it once or twice and the phase is over so he's unloading it for something else. I don't know how the phase could be over so soon when the peak riding season hasn't even hit but the wealthy people who buy cars, houses, boats, and motorcycles just for the heck of it, think and operate on a level I don't understand so I can't speak to motive in those scenarios.
Since we may have people like that in the forum, let me define my idea of wealthy as to not start something or offend anybody. If you could go two or three months with no income and still be living comfy, you're considered wealthy IMO.