As mentioned Uniregistry com now branded as DAN.com is a great place and 10% commission, SEDO.com is another market place but the commission is high.
Afternic.com is another huge one but again the commission is high but the cool thing about Afternic is that it integrates with almost all domain providers such as if someone searches your name on Namecheap for example it will have your domain listed with "make offer" or BIN buttons.
SEDO does the same actually but I believe it has less integrations with domain registers.
If you want to sell it faster and willing to come down to Wholesale pricing I recommend dnwe.com, namepros.com, nameliquidate.com.
You can also list it on brandbucket.com or squadhelp.com but overall do your own research, DAN has the lowest commission, Namepros.com is free but these don't provide the exposure as services like Afternic.com
Then of course there is out bound marketing.
And since you got a casino name as you said you can try and reach out to: SportsBettingDomain.com
Best of luck mate.