Double merle aussie question.?

I've been looking for an aussie mix forEVer. Finally found an absolute darling one today—but to my dismay, she is a blue merle–dad is purebred blue merle and mom is blue merle, shar pei mix. My question is: with mom being a mix, do we still have to worry about the double merle issues? I'd like to take her just to get her out of a household where they obviously are careless breeders, but they are asking $200 and I say they are crazy. I also have too many little people in my house to expect a dog with handicaps to function well. Guess I will continue to search, but I am curious on the mixed breed thing.
Well in my defense—I'm NOT getting the dog, I only said it was tempting just to save the poor little thing from careless owners who obviously don't spay and neuter and I've looked into fostering and am unable to do so as we are rural and the orgs I've looked in to all require a fence to foster and lastly, I check our local rescue often in hopes of finding a good match for our active house. Our furry daughter now is only 8, so I guess I have time to keep looking–but did just want to find out a little more about the mixed breed thing. I also wondered–in my sleep–if a blue merle "something else" (catahoula, border collie) were to breed with a blue aussie, can that create the double merle issue as well, or do the problems arise more in a purebred?

I'd look at how much white is actually on the dog. A double merle will be almost entirely white. A blue merle CAN (not necessarily should) breed to another blue merle and give blue merle and double merle pups. You're right about them being crazy asking $200 for a mixed breed. Try talking them down.