Hello and welcome
Yes there have been high-end domains sold here but there are steps you must take to have your domains listed.
You would first need to add your domain to your profile as an owned domain. Once you’ve done that you can enter it in contests but you’ll only receive the prize amount if it is selected as the winner. The only way to receive more than the prize amount is to submit that owned domain to the SH marketplace. If SH approves this domain you’ll then need to accept their commission terms. If you accept, your domain will then be listed exclusively on SH and a complimentary logo will be created and SH will exhaust it’s marketing efforts on getting this domain seen and sold. Once it goes live you are able to submit this domain in appropriate contests, however, you will only get the premium payment if the contest holder is open to premium domains, which will be stated at the bottom of the contest brief, if the contest holder is not open to premium domains and you submit your marketplace domain you will only receive the listed contest prize amount.
Now, that being said, this may be changing very soon. But at this moment that is how it works.
As for the limited amount of contests you are able to participate in, you need to continue participating and you will eventually earn a higher level of trust and you’ll be able to participate in more and more contests and gain more privileges. I won’t go into detail but some newbies are here for the wrong reason and this helps roadblock their intentions.