I've used Facebook, Tradesy, and Poshmark. As much as selling makes me nervous, I haven't had any problems with any of my sales. Really the only people I don't like selling to are resellers because they tend to be the pickiest and least grateful buyers I've dealt with. Not saying that they're all like that, but the ones I've dealt with were. Usually the people who are buying are just like you; people who are fans of nice handbags and want to get a discount. With any selling platform I use, I always take lots of pics, film myself before and after boxing, and keep shipping receipts. That's really it.
Tradesy: I like this one the best. If someone makes a return, Tradesy will usually take it. However, there have been a couple sellers who have had their returns given back to them and the buyer was refunded. Commission is steep (almost 20 percent when you take into account Tradesy fees plus bank/Paypal fees) so oftentimes you have to price accordingly to make the most money.
Facebook: Not my favorite but I don't think it's totally bad. You can post as many pics as you like in your listings and you can always ask for references from buyers in case you're not sure about them. Like you said, you have to be diligent with "bumping" your listings because they do get buried. Occasional low-ballers or people who ask for payment plans. I think it's technically more "dangerous" for buyers to buy on Facebook as opposed to sellers. Having a Paypal account is a plus and is preferred.
Poshmark: My least favorite selling platform. Poshmark fees are a flat 20 percent, with the exception of items that are $20 or less (I think...?). People LOVE To lowball there. There is also a picture limit, although they finally increased it.
eBay makes me nervous, but there are plenty of people who've used it and haven't had any issues with it. The lowest fee cut I've seen (roughly 10 percent). Unlike the last 3 selling platforms, feedback is available for viewing.
Bonanza: never tried it because traffic is too low, but I've heard people who've preferred this over eBay.
I used to do the consignment route myself (and prefer it), but the offers have been so low lately I couldn't make myself do it. If you think you won't get a huge loss, it's best to use
Fashionphile and Yoogi's.