I get good customers from Craigslist, but I also get price shoppers. When someone calls, I always explain the process in terms anyone can understand, the estimated time involved, the quality of the products used before giving a price estimate. If I can tell they are on the fence, I'll get an email address and send them before and after shots of previous details. For the ones on the fence, most of the time this does the trick. However, a lot of people just thank me, and hang up after they realize they can't get a full detail for $50.
One thing I have found is that a lot of customers that call me through Craigslist have had bad experiences with previous detailers. Typically, by showing up on time, having good communication, acting professional, and turning out a top notch car, these people are usually very appreciative and become good, long term customers.