I have had plenty of sales on Namecheap marketplace over the years, fairly regular too, like maybe 1-8 sales every 1-3 months depending on how many domains I have at Namecheap. However I have been using Namecheap for more than 7 years now and have never made a sale of more than $200 and even that happened only once. Low priced domains are what tend to sell best there (for me), usually my sales are in the $5 - $30 range. I mostly list domains that I don't want to keep on there and don't bother with higher priced domains (high xxx to xxxx). They charge a flat 10% commission on all sales.
Yes, you need to wait until you have accumulated at least $100 before you can request withdrawal by PayPal but at all times you can withdraw any amount you've earned from sales to your Namecheap balance to use for registering new domains, renewing existing ones etc.
Towards the end of last year, I contacted them to see if I could use auctions for my domains and they confirmed that only expired auctions were available for now. Users can only sell via BIN listings.
Unfortunately, they don't offer any landers which is a real shame in my opinion. A few years back I remember they had a free page builder tool which I used to create simple landers for some of my domains but I don't know if they still have this.