FWIW/FYI - if you spend enough time and post enough to figure out a few other acronyms (BOAL and WKR as examples), you will probably do better. Without feedback it could be tough. Otherwise GLWS (good luck with your sale).
WTS - Want to Try to Sell. Typically this means someone has an item that they haven’t used at all. If it’s Sitka clothing, you can usually count on the pieces being used only for “trying on”. Of course the tags were removed so that proper fit could be verified. Usually these types of items are list for full MSRP or above - because, you know, supply chain issues.
WTT - this one is tricky. Not sure what the abbreviation actually is, but I assume these people are just looking for friends.
WTB - these are mostly people who are looking to make a donation to the scammers in our midst.
SPF - this is a modified version of the WTS outlined above to let everyone know that the seller wasn’t actually asking too much for their item because they found a user to commit to maybe purchasing said item, but they need to let their wife get home first to make sure it’s ok
YMMV - Internet talk for adding an “…I don’t know though…” at the end of a statement which sounded very educated and well researched.