I have sold a bunch of Star Wars stuff through marketplace. There is nothing that restricts getting paid before shipping. Perhaps they do if you pay through facebook itself. Honestly FB only gets involved if you are trying to list something illegal. The bots will generally block a listing for a replica blaster, they have even blocked lightsaber hilt replicas calling it a weapon.
As for listings, I always offer shipping. I generally list items as $XXX or best offer plus shipping. All my payments have either been cash in person or paypal for items I have shipped. I have always been paid first before shipping an item. Overall, it is so much easier than ebay and you are only paying fees for paypal payments.
You do find you get a lot of people who want something for nothing or people that just don't respond. Essentially any listing you click on has a standard "is this item still available" message button. You get a lot of those messages from people who then don't respond when you tell them it is available. You also get a lot of "I'll pay you $50 shipped for the item you have listed for $100 that will cost $25 to ship". They are quite persistent in stating they have the money ready to go and that even though the item has sold on ebay $100, ebay and paypal takes fees, so their $50 offer is really generous. Also they act like they are doing you a favor by having you ship the item rather than meeting to pick it up. Also be wary of overseas buyers. I have made a lot of great deals overseas, but also a lot of headaches dealing with them. No offense to Australians, but a lot of them are a huge pain in the rear. I have had countless inquiries about multiple lots of stuff. Put everything together to get a shipping quote, then deleted stuff to get a lower quote, to then finally say, "oh, what about import tax, I can't offer as much because I have to pay that". As a general rule of thumb, anything over around six pounds is $100 to ship to Australia. Additionally, USPS only insures up to $200 to Australia. UPS and Fedex do not want to ship internationally. Every quote from them is $500.
So overall, it is quite doable, especially if you get local buyers. At this point, in past year to year and a half, I have sold the following:
All my carded figures from orange carded POTF2 through the beginning of the black series (1995 to 2008 or so)
All my battlepacks, deluxe figures, exclusive figures, etc. (essentially everything that isn't a standard carded figure, but not a vehicle)
All my loose figures (bulk detail to a guy in the UK - he even used a parcel broker, so DHL came to my house to pick everything up, I just had to box it, print out the labels he sent, and fill out a customs form)
A majority of my loose vehicles and beasts (still have several lots listed)
A majority of boxed vehicles and beasts (again, all remaining items are listed, I'm down to 42 items left grouped into several lots)
30 Sideshow 12" figures and counting (starting with prequel items, 19 figures left plus 60 OT items, which I will probably keep a decent amount of)
Several Master Replicas items
Once I get all my listed items sold, I'm moving on to attempting to unload my Hasbro 12" series, then I'm sorting through Legos to see what I want to keep.
Just know that this does take a lot of time and effort between sorting through stuff, taking pictures, and making listings. My dining room has been a staging area for the past year or so. Stuff comes up from the basement, then I take pictures and make listings, and just leave it in the dining room until it sells. You will probably get inquiries from dealers who will offer to buy everything, but that will really lowball you. At this point, I have made a really decent profit overall, especially since I have sold stuff that I never thought I could unload and the vast majority at cost or above.
So easy answer, definitely go with FB marketplace. It is really nice when you make a sale and just have to drive a few miles down the road for an in person pick up. Otherwise, definitely get a digital scale. I got one on amazon for $25. It has a 110 lb capacity and I have weighed boxes that are 24" on a side on it. Also remember that USPS are supposed to measure a box that has any dimension greater than 12". They always remember on very large boxes, but not always on the smaller ones that they should be measuring. That will up the shipping price. Also, they have a max size. The 24" a side boxes are too large to ship via USPS and have to go UPS.
