Most companies will charge a basic billing fee, usually around 3.5-5% and will also provide "management" for additional percentage. All in billing and management fees are around 7-8% depending on the profitability of the facility and sometimes are much higher if the facility doesn't generate a lot of collections. Basically all the companies I'm aware of charge a percentage of collections.
When it comes to billing for an ASC it is very difficult compared to a clinic. Every case is extremely costly and there are huge costs associated with each surgery. There isn't any room for error. Insurances are a lot more stringent on the claims as well because they are paying out so much for each one of them. The management side of the ASC is a bear as well because there are so many regulations and hops to jump through. Fall out of compliance with any one of the requirements and you are at risk of being shut down or losing an insurance contract which could sink you. Things like have you done your monthly generator checks and logged them correctly, is your humidity in parameters and logged correctly, when was the last time you did a fire alarm check and did you document the appropriate staff attendance that was required, did you have all required medical equiptment inspected and did it pass and can you produce the report when asked...it's a lot.