When to Stand Your Ground and When to Backdown

As someone who hates conflict I often find myself backing down when it comes to couponing instead of standing my ground.
Like the other day when I went to CVS to do the Olay deal. The manager told me that "one per purchase" meant one per transaction. I know for a fact that she was wrong but I didn't say anything.
Or like when my total is $2.98 and I have a $3 Q. I know which stores are supposed to adjust the value of the Q to make my total free but I ALWAYS get the cashier who doesn't know what they are doing and tell me, "you can't use this".
I always want to speak up and tell them they are supposed to adjust the Q down but never do.
Things like this happen all the time to me when I coupon and I rarely ever speak up. But I am going to start speaking up! If it is something that I truly need, why would I let someone rob me of money that I shouldnt have to spend just because they do not know their own policy. (without being rude, of course)

This is where having a copy of stores coupon policies with you is SO important. If you are able to show them their own rules, they have no reason not to follow them.
I personally keep a copy of the policies on my iPad that I can pull up. And I have done so before, and it works.
Also, if you ever have a bad experience at a store, contact corporate. I have contacted Walmart corporate twice by email due to awful experiences.

Now there are sometimes when I have had such an awful cashier that I decide the hassle is not worth it, that's when I politely say "thanks, but I don't want it anymore" and leave.