I always ask a new client "How did you hear about us?". Any referal, and/or person who saw our operation is most always going to be a new client
Many people just thank me for returning their calls. YP ads will get people outside your target are, people looking for el cheapo too, but you can get enough good leads to warrant your ad. Screen them as much as possible over the phone and judge for yourself if its worth a looksee or bid. You should always at minimum have name and number in case they remember your company name and are looking for number to call.