Hello,
What are the advantages of selling a Domain through a Market Place than through a self hosted page showing "This domain name is for sale. Fill the form...".
It's not really an either/or situation; you can still have your own landing page for the domain, as well as having it listed for sale at various marketplaces. Most marketplaces don't require you to use their parking/landing pages. I create my own landers, but list my domains for sale on the marketplaces. Right on your landing page you can include a link to the sale page of whatever marketplace you have it listed, if you wish, though I don't do that. I prefer to have just my email addy on the lander, and if I enter negotiations with a possible buyer and they want to go thru a domain escrow service, then I'll send them a Sedo link for the domain.
However, if your domains aren't parked with the marketplace but they receive an offer through that marketplace, some marketplaces will charge you a higher percentage commission. For example if you have your domain parked at Sedo and receive an offer through Sedo, I think they take 10% commission of the sale. But if that domain is not parked at Sedo when an offer comes in thru Sedo, I think they take 15% or more commission.
However, parking your domain at Sedo sucks big time, now that they are using the very spammy-like zeroclick ad platform. Most visitors to your parked page will never actually get to your parked page but will be redirected via zeroclick to another advertiser's site. Which means most visitors will not see your 'this domain may be for sale' on your parked page. So if the 'for sale' sign on your domain is important, park it with a different parking provider or marketplace, or create your own lander.
We all have different preferences. You can park your domains at a marketplace that allows parking (like Sedo, Afternic), or create your own landers and just list the domains at those marketplaces, or just use your own landers and don't list at the marketplaces. Whatever combo you like.
But it makes sense to do both; creating your own landers allows visitors to see whatever info you want to place on your site to help sell it, and give it your own custom look, logo, etc, and helps search engines see your site/domain better than a parked page does; and listing it on marketplaces makes it visible to the many people who search for domains by keyword on those markets.