Regarding Western Union usage, the downside primarily seems tied to sending funds via that service, not receiving them. I can't see a downside of using WU as a means of receiving cash payment picked up at a local WU agent.. Might be better as a seller than PP in that the buyer/sender pays the fees, not the recipient/seller. Seller gets cash so no PP chargeback risk nonsense.
However, be extremely careful to whom you give your bank account info. Better to have cash sent to a local Western Union agent that you can pick up as opposed to giving your unencrypted bank info out to a stranger (which you shouldn't do unless it is an account that you keep virtually empty). I gave an account number out once for a wire transfer on a Rolex sale but the buyer had impeccable references as a Rolex collector. Not sure I would ever do that again though. (And I also had a guy insist on sending me hundreds in cash for rackets via carrier once. I wouldn't recommend that practice either.)
Bottom line: Never wire money to someone you don't know or trust 100%. However, if someone is willing to wire you cash for pick up at a WU agency based on your stellar reputation as a seller, no problem.
These are the most common WU scams:
Common sense stuff, but a good reminder:
This also points out why it is a very bad idea to post your email address within your classified ad. By doing so, you are inviting spam and phishing/fraud. Don't post your email address; instead, make the other party contact you through the TW system. Just make sure you have enabled messaging through TW.