I wouldnt use CRI unless you are a CRI Approved Service Provider and using CRI Approved products...you could be opening a can of worms and losing a client cause you'll have to explain your way out of not being or using....
I wouldnt use Stainmaster if you are OP only, for they recommend HWE....
Personally, I feel a spotting guide is not needed. You should be leaving a bottle of spotter and training them how to spot at home. If they cannot remove, then call you. Thats the best advice you can give your client....