Up-Front and Initial Payments
On one or two occasions we were asked for a small (10%) payment just as the work began, because the cost of materials involved was high. More frequently we were asked for stage payments as work progressed, but these never exceeded the value of the work already done.
We never paid anything in advance of the work beginning, or at the time of accepting a quote, and we never paid a large percentage of the total upfront. Neither should you. On the other hand, we always paid bills promptly when they arrived. Most artisans are small businesses, and can do without waiting months for you to pay. Word will get around the other tradesmen in the area pretty soon if you are a slow payer, or dispute your bills unnecessarily.
Never pay a greater amount of money than the amount of work that has been completed to that point in time, except if paying for materials already bought and supplied.
Subsequent Changes in the price
Usually, the price quoted in a devis and accepted, is the actual price that you will pay. it is not a variable estimate to be changed at will, just because things worked out slightly differently when the job was under way. In normal circumstances the only thing that can change the final price is any changes that you have discussed and agreed with the people involved. Any change in price should have an additional devis to go with it.
I should admit that we didn’t always follow this rule, when we were confident we could trust someone. When we agreed with our plumber that we needed three bathroom radiators instead of two, we were happy that he would add the correct additional cost on the final bill. Most changes are less easy to quantify. If you decide you want the rear wall of the house repointed instead of painted, or a bigger septic tank than you had originally planned for, you should get an additional quote in writing.
Overall, this has never been a problem for us in France, where a devis is more like a ‘fixed quote’ than an ‘estimate’.