If it's a bid job that is it a bid.
If you are discussing a job with a customer, it is ok to haggle a little just know your costs and do not give anything away that cannot be made up later.
For those jerks that want to play games and ripp you off after the work is done see them in court. Also get to know your states lien laws. I always file liens on slow pay and those who argue about price. Also make sure that the final payment is due upon final electrical inspection not completion of job. Some owners/Gcs use there punch lists to demand extra work and as an excuse not to pay on time.
