Find out exactaly what they are looking for, be sure you can provide it.
They may want 8 recess lights, put on an existing circuit, and another contractor told them it was no problem doing this, if after you check, and determine it will overload, then explain that it will cause an overloaded circuit, and if they insist you put them on the existing circuit, you have a problem customer.
You may ask if they have a budget price for the job, if they say no, then it might be, they din't budget for the job, they may not have the money to do the job.
Tell them how long it will take to do the job, if they say "that long", then they are not ready to do the work.
Look at the home, has it been kept up or is it run down, did they just move in, or did they let it run down?
They start by telling you, how many contractors have been there already.