Before you accept a quote which is much lower than the others check that they understood the quality of work and materials you want. If you don't understand a quote ask for help from your local Citizen's Advice Bureau. GST A quote must include GST in the price, or state that GST is not included. Eg, you take your watch to a repairer because it won't go. They say they will look at it.
Some quotes are free.
However, it is common practice to charge for a quote, so check this out with the seller. If you have the work done, some sellers will take the price of the quote off the repair bill. Eg, you accept a quote to re-line your bathroom in water proof wallboard. When the old lining is removed it is found the timber studs are rotten and must be replaced. The seller must get your permission to carry out extra work.