I've been happy with bid-to-call. It's super cheap and some of the calls are good. Most are not potential customers, but that is true for clicks, too. That's part of doing business. Overall bid-to-call has been a good thing.
However....a couple of the AdGroups I had it on started getting a bunch of calls. These were low activity AdGroups, and there were most calls than clicks (normally the ratio is about a hundred clicks for every call). The calls were under 30 seconds, so Google does not charge us for them. I am not worried about the cost from Google. I am worried about the labor cost for my client who has to answer the phone. Too many of these low quality calls becomes a nuisance.
To remedy this, I paused the AdGroups that were generating these calls (at least, according to Google these AdGroups were generating a lot of calls.) After pausing, there were zero clicks. But the calls continued to come in! Google still reports under 30-second calls from these two AdGroups!
Is this a new form of spam or fraud? After worrying about fraudulent clicks for years am I now going to have to worry about fraudulent calls.