i have done a lot of the indian restaurants around my way and have to say as long as you let them beat you down on your price they always seem happy, which is why i always quote 20% over, i know but the time i leave it will be cheaper by 20% lol.
The chinese restaurants are a different kettle of fish, they always want it done for next to nothing, and its ok to say that when we are quiet we should turn down any work, but there has to be a limit, i made the mistake the first time i did my local chinese of quoting a way too low price, thinking it would take half of the time it actually took me, and after paying for the fuel, and the chemicals, i think i was on less than minimum wage, so it worked out at stupid money and i ran the machine for quite a few hours taking in all the crap for little to no return