looking through Facebook Marketplace, I see a lot of ads that read "ships to you". What kind of luck has anyone had with those ads?

I haven't tried it in buying or selling. My understanding is FB holds the $$ until the item arrives. That could get a bit sticky IMO especially with the current state of Shipping or mailing anything in addition to the buyer claiming they either 1. They didn't receive it or 2. It was misrepresented.
Myself, as a seller I wouldn't like the idea of them "holding" the $$. maybe someone with a bit more knowledge /experience will chime in

I tried it twice, both with non-automotive items (camera bags):

1: Bought, paid with PayPal, seller sent me tracking # within 24 hours. Item arrived in 3 days as advertised.
2: Bought, paid with PayPal, seller changed item description to "pending" and then ghosted me. Sent 3 polite Messages through FB, no response. Filed a claim through FB and got a return message that the seller has 7 days to ship, can't do anything until then. On the 8th day I filed a claim and the $$ was back in my PayPal account in 2 hours.

I haven't tried it, but it sounds basically like the Feebay scheme, only I guess it uses PayPal, like Feebay used to.
The Feebay deal, BTW, is no better on fees (as they claimed), but just another thing for sellers to manage.
FB seems to have more clowns than even CL, so I'd prefer to deal in-person, but sometimes you can't.

one thing i have noticed on some of these adds, is the shipping "quote".
example would be : "ships for $5.50", when anyone with any kind of shipping experience would automatically know that quote is nowhere close to be an accurate shipping fee for the item at hand.
that makes me a little leery of the add and seller.
maybe that's just me ?

One thing I have noticed is that many are large items, water heaters, stoves and other appliances. I have wondered if they had some sort of "drop shipping" arrangement with manufacturers (that assumes they are legitimate). Obviously, we are talking about some sort of truck transport.

I sell on Facebook marketplace all the time. It's been great as a seller. If you want something that says "ships to you" then place the order through the ad. It takes your payment. The seller gets the notice of an order. If they accept the order, it processes your payment and generates a shipping label. I have had zero issues with shipping through Facebook. The shipping is based on a weight range so for the seller, it is much easier because I don't have to enter and figure dimensions. It just simply goes by weight. Also, the shipping rates are cheaper than I could get through eBay or on my own, I just have to use plain packing and not the USPS labelled packing. The seller packs the item, prints the label and ships the item. Every label has tracking so both the seller and buyer can track the item. Once it arrives, Facebook sends the seller the money. Yes it takes a couple weeks total sometimes but usually it's a week. The fees to sell are 5%. Often Facebook offers free shipping to the buyer and zero fees to the seller. My opinion is that it is was better than eBay, both for having lower fees and for ease of listing.

so marketplace is kind of like feebag started out like ?
you send the money to marketplace, then marketplace sends it to the seller after the buyer gets it ?
i'm really confused now.