It would help if you provided profit/loss figures, a balance sheet, traffic states, list of assets etc. Making people come to you for these details will deter people making an offer since its quite cheap to build your own site these days.
Not true. Yes, it's quite cheap to build your own... I'm sure a lot cheaper than taking ownership of an already established casino with custom games
but requesting potential buyers to contact them shouldn't be a deterrence, at least not for serious operators.