For me, having the fabric washed (and ironed) before cutting (preshrunk and excess dye removed) is extremely important.
Would you be willing to include that in your service? And if so, what would you charge?
The next question, would people be willing to pay it?
Would you charge by yardage plus X amount per piece (sort of like how paypal charges?)
Would you finish the edges before washing?
Would you totally refuse to mess with washing before cutting?
I'm thinking that some people don't wash fabrics before cutting just because it's a hassle to do any laundry.
Would you include some extra fabric to cover mistakes?
Overall - I avoid kits because:
1) I like my fabrics washed before they are cut
2) I like having extra (excess) fabric available in case I make a mistake (and I usually do)
3) I like to have flexibility to change my mind during the process -
4) I get upset if the kit doesn't end up looking like the picture (missing pieces, wrong size cuts, poorly written instructions, etc. would be contributing factors - I would not blame the kit if I was the cause of the goof)