You are very correct, to get reputation the new company needs to partake in aggressive promotion of their brand in every social media handle and in the forums such as this one but not every company that promotes sustains their reputation. Some can spend huge amount of money for promotions but one mistake will their reputation within a short period of time. So it is better to have a formidable team that is very reputable such that after you do your promotion there will be no doubt to continue using your site. A scam company like 1x bit do good promotion but still their reputation is bad, so when good customers are coming others are leaving, it is a problem to the company .
Don't mix advertisement and reputation, those are completely different thing.
Advertisement only have purpose to reach people as much as they can in order to get new people which interested with gambling to gamble in their casino. While reputation is the trustworthiness of the casino, a casino doesn't need to launch advertisement, they can just stick with their current gamblers and never scam, slowly their reputation will built up and anyone will believe if the casino is legit.
A scam casino who run a big advertisement isn't built or recover anything about their bad reputation.
in this forum case a new casino when they hire a good campaign manager and they run a long signature campaign. something like 6 months and constantly this new casino offers giveaways and contests here on the forum and all people receive their payment without delay and when they win contest that person is soon paid, when they do promotions the customers soon benefit from this promotion so this casino gets good reputation. imagine a new casino that sponsors the premier league Vs a new casino that creates an ANN thread on this forum and has never sponsored anything, never run any signature campaign, which casino would you use? I would use the new casino that sponsors the premier league and the reason is simple: the new casino that sponsored the premier league will not risk making a scam when everyone knows the name of the casino owner because in the announcement of a partnership between the casino and the premier league casino owner had to leave his real name, and also this casino owner will not want to destroy his reputation by scamming