I called for an estimate for major work that needed to be done (along with 3 other plumbing companies). Someone came out for 15-20 minutes, looked at my cement slab, never entered my house and wrote up an estimate for $4400. My insurance adjustor happened to be here at the same time and mentioned that he was pretty quick in giving me an estimate. The 3 other plumbing companies spent approx. 45 - 1 hour at my house, inside and out, with no charge. I suggest you notify your potential customers there will be a charge for the estimate prior to arriving, or at least upon arrival, but definitely before you send a bill.