Tattooing over scars

I have an appointment today to start a rather large project that centers around a very large scar.  A lady I've tattooed before had back surgery and has been left with a scar that wraps around her waist like a belt as well as about 4 inches added on to her butt crack.  She has very dark skin and the scar is not very noticeable , but she has insisted on going forward with this project , in spite of the fact that I've estimated the final cost to be well over $1000 and potentially 4 sessions (or more depending on how she sits).  Today we will start the outline.

I've had very good luck with tattooing over scars, but it's always a gamble.  There is never any guarantee that the pigment will hold the way it should and that makes things very tricky.  We're going to be putting big, stylized flowers and vines ~ like a beautiful garden ~on her and I am hoping to be able to use a bit of color, if only red and green.  I won't know until I'm actually into it.  I hate not being able to promise her what the end result will be, but that's the nature of scar tissue.  Fickle and unpredictable.

I do have some photos of her scars and w/her permission, I'll post here and show updates.