I can't provide legal advice, not qualified at all, but I have a couple ideas you might want to consider to tighten up the language and eliminate some potential grey area. I'm pretty sure ultimately you're not going to be made whole, but personally, and after that cocky message and the admission of deceit, I'd drag his arse in to court (or get a default judgement) just on principal, even if ultimately ineffective at righting the wrong.I'm not looking for a legal advice, but I welcome anyone's input as to whether it is on point, or anything is lacking:
I don't like the facebook marketplace mention, not sure it is helpful, and might bring jurisdiction into question. Ultimately you bought these in a face-to-face transaction in the same county you're filing in, correct? I might try starting something like this instead:
"On Dec12 2024, the defendant sold me four gas cylinders for Scuba use for $X, under the pretense that they could be legally filled with air in the USA and had recently been used for scuba diving in this country. Defendent later admitted that he was aware at the time of sale that they could not be safely and legally used or inspected in the US, as they lack required DOT certification and were actually manufactured expressly for overseas use."
On a similar note, I might tidy up that last part. You're not asking for your money back and to keep the product, I wouldn't leave that open for interpretation. You're not trying to punish the seller, just unring the sale as it was made under false pretenses:
"4) refused to take the product back and return the cash"
Before you do that though, do you want to reach out one more time with a "Dude, we both know you're clearly in the wrong here, do you want an opportunity to do the right thing, I'll let everyone know you came to your senses, and you take these tanks back?"