Marketing is one of the keys but what matters most is provably fair games, transparency, trustworthiness then active costumer support, quick deposit and withdrawal now, with all these it would attract more people and also gives room or space for effective marketing.
When gamblers sees all these are something very free from the casino marketing won't be a problem the casino itself would carry out the marketing of a thing, meaning those people who are gambling on the site are same people who would keep referring their friends to come make use of that gamble site.
That is right and most cryptocurrency online casinos are already aware of this and will definitely continue marketing their platform regardless of how big their may have become, a good example is Bc game and stake and the rest of the other known cryptocurrency casinos that we have here, one of the fastest way for a casino or any business to grow audience is through active marketing and attraction with their community.
Now, with little efforts of marketing they will become successful, and yes funds is need normal for pay out since most people could win above the casino back balance then they must source for additional funds to make payout to the gamblers. Now, this now draws to how some casinos limits stake amount, winning amount or maximum odds to be allowed to stake on their gambling site in order for them still remain in control of their payout instead of them to go bankruptcy.
This little effort cost alot for most start up so we shouldn't refer to the financial efforts and commitment as little efforts, it's take alot to make a casino successful and only marketing alone can't give that success it requires alot of other factors that that casino will have to bid in with full focus.