Hi there,
I'm not a mobile, but would definitely advise you to include a finish.
You need to see the cut/colour yourself before you leave, to make sure you and the client are happy with it. Other wise, you could end up getting a call later saying it hasn't dried up as they expected it to!
Also, as you have mentioned....some of them are after CHEAP AS CHIPS.
Now, if your O.K. with that....fine, but I'm sure, like most of us professionals, you have a real pride in what you produce, and that sense of pride comes at the end, when we see our finished 'DO'.
This finish is also our walking advertisment. If they are left to 'scruff dry', lets be honest, it will never show our work to its best advantage!
In the salon, I do all inclusive pricing...no hidden extras, clients appreciate this, I get job satisfaction, they leave looking gorgeous, and it keeps this profession...PROFESSIONAL.