First, I am surprised nobody has shouted how dare you not Quarantine the snake, based on the pic you posted with your Pastel
Second, I am going to say it probably is a Cinn, but just a C Grade Cinnamon (and no, the C grade does not stand for Cinnamon, but low quality). As for the price, if the buyer and seller are both happy, then it was a fair price. You only need one person who likes your animal and your price to make a sale. Most Cinns have a reddish color to the side patterns, and the nice flames or blushing at the bottom coming up. This snake has the blushing and flames, but I am looking hard to find the red coloration that gives the Cinn its name.
Third, I am surprised (unless it was in the orignal ad, that I did not see) that nobody has brought up the history of this snake, like what is the history? Is it a CH female, is it from a wc clutch, is it from a known line of Cinny and just the ugly duckling baby? If the snake was from a known line, then it probably is a Cinn. If it was a CH animal, it might be, might not be, and I hope it was sold as such. If it was from a WC female that laid her eggs in captivity, and people are guessing what it is, and decided upon cinnamon, that is something totally different.
If it is a genetic Cinnamon, it is a low quality one, in my opinion. That is not the end of the world though, because when you have breeder animals you want your males to look spectacular, and the females to look as good as you can afford at the time of purchase. If you want me to explain this, just ask...
If it is a CH animal, it is a dinker until proven otherwise, in my opinion. If it was wc, or the baby of a wc female, it is probably a dinker or, if there were better examples in the clutch, and there were obvious cinnamons in the clutch, I guess it could be called a cinnamon.
So, what is the snake's history?