When quoting for jobs I offer either an all in quote for labor or a daily rate. Longer, bigger jobs usually require a fixed price. Clients will often want to provide materials, but I will orgainise this if necessary. All quotes are VAT free (as I am not required to be VAT registered in France).
In France, a quote is a contract to do the listed jobs for an agreed price. Normally, the devis/quote should be signed by both parities. Often (especially on larger jobs) things will be added on or a client may change his/her mind about what is to be done. In this case, I re-write the quote adding on any extras in labor. Overall, the French devis system is to avoid ambiguity or conflict – said work is done for said price. Most quotes require around 30% up front, although larger jobs need a scheduled payment program.
Certain jobs may need to be sub-contracted to different tradesmen (plumbers, electricians, diggers etc). In this case, I always ask the clients accord or for their own traders where possible.
Working at someones house is a question of confidence (who is going to be on-site, when and with whom). Money is also ex- changed, thus all parties should know exactly what is expected of them. Overall, my aim is for a win-win situation, happy client, happy trader.