maybe scam / maybe not. I would take it further if you want to sell.
In Canada at least, a cashier's check is a check guaranteed by the bank and drawn on the banks own funds to you (not buyers funds). So ask buyer to send you a picture of the bank draft. It will have Banks name, address, and its serial NUMBER, etc..... If the Bank draft is drawn on a recognizable American based Bank (not something like bank of hong kong or bank of malaysia which you cannot check on) you can simply phone the Bank to ensure that the bank draft number is legit and funds are truly in the Banks hands. Better yet the local branch in person.
If dealing with a recognizable bank with local offices (BOA, Wells, etc...) and bank can confirm THEY issued the draft you are safe. Would never touch it if cannot verify with local branch so buyer has to provide on appropriate bank. If bank is forgeign and check cannot be made then scam for sure.
I have done this many many times as some of my old stuff gets sold to people too far away to inspect but unique enough they are willing to trust and take a chance.
For sure 100% right to be worried just do your due diligence with the issuing bank. Now if paypal, private cheque, Vemo, etc... wouldn't touch it with a 10'pole.
Cashiers cheques on legit Banks that have a local branch near you that can be independently confirmed by you in person should be fine. Like 2 step verification.