In my opinion, the most important thing is honesty and openness.
Representatives of the bookmaker's office must constantly conduct a dialogue with users and customers. It is necessary to promptly inform about your plans, talk about current activities, respond to criticism, and admit mistakes.
The client will forgive the bookmaker for any mistake if it is promptly recognized and corrected.
Feedback from users will allow the bookmaker to improve its activities and become better.
I don't think forgiveness will be given in those cases, just that they at the very least know that the casinos openly admit to their mistakes, and are willing to compensate for it. That in itself brings about a reputation that the casino was made for the players and their services are for the players.
if they can't afford spending large money in marketing, they can still earn credibility thru time. it may be long and hard, but these players once you get their trust, they will be your loyal players. the reputation of the casino or bookie is not earned overnight. so that's fine if they won't run high-reward events. but at the beginning, at least hold some small events or bonus program. it doesn't need to be expensive reward. this is just to attract potential players. and for me, it is better to run bug bounty program rather than promotional activity. this bug bounty will further help improve the site itself and it will show that the site is sincere in giving good services to the players.
Players earned through marketing are mostly people who are in it for the bonus, they'd probably leave at first notice after said bonuses die down so really, players who join a casino through their credibility should be the market that a casino should target. If they can do marketing though, then all the better imo.