Are you speaking directly to the dr? I would be asking if they are having any issues. Most offices that do the billing in house have some issue. For many it is turnover of staff. If that is the case I would come back with it's hard to hire someone with experience, and even when they have experience you really don't know if they are good. I also state that it saves them on having to find someone, saves on payroll, taxes, etc.
If they have someone and that person has been there forever, they are less concerned with those issues, but they may have other issues. That person has other duties that take them away from the billing. In this case I push the working of the aging report. Most offices do not get to this, and a lot of money is lost. If this is the case I tell them that our fee is usually covered by what we collect for them that they are currently missing out on.
There are other issues with in house billing like keeping up with changes, clearinghouse issues, etc. Also, the person may be good, but not understand coding. Or maybe they don't know how to handle denials or don't have time for denials.
The key is to find out what isn't working and show them how you can fix that problem.
If everything is working perfectly (which it hardly ever is, but sometimes they won't admit it) move on to the next one. It most likely will not be a good account.