In Australia there are two types of bookmakers: corporate bookmakers and rails bookmakers.
Corporate bookmakers
Corporate bookmakers are typically your household names. They advertise extensively on TV, and have large customer bases.
While matched betting with a corporate bookmaker, your activities are likely going to go unnoticed for longer due to the sheer volume of bets they process.
Because they're large (sometimes public) companies, they can be generally trusted to play by the rules and honour wagers.
Rails bookmakers
The other type of bookmaker are rails bookmakers. When watching racing in-person, these are the bookmakers you typically see operating at the track. They tend to have a more localized focus and do not offer the same breadth of markets as corporate bookmakers.
Rails bookmakers can be more sensitive to individual betting patterns, which means your activities may be noticed more quickly. They may also have different rules and practices compared to corporate bookmakers.
It's important to note that the prevalence of rails bookmakers in Australia exists in no small part to service the market of degenerate gamblers who have self excluded from the corporate bookmakers.
Because of this, rails bookmakers may be less inclined to accommodate matched bettors, and may be more likely to restrict or close accounts that they suspect of matched betting.