Toner Too Dark -- WHY

I always make it VERY CLEAR to my colorlist that I want my hair VERY LIGHT (blonde). Well, I had my hair done last week and right away I could tell something wasn't right (it was still wet). I thought she hadn't put the toner on but she had. It's definitely darker than usual, and I do not understand why. (No, I didn't ask her. I can never really tell what's wrong until I get home. And no, at this point I'm not saying anything. Maybe I will when I go back ... .) She KNOWS I want my hair the SAME EVERY time. Anyway, to cut to the chase here, do you think she either used a different brand of toner than she usually does or maybe mixed it up differently? I always think that when my hair looks different. I just don't trust them. Last time when she did my brows they turned out WAY DARK -- I looked like I had two caterpillars on my face (lol). Well, she just could NOT understand why -- she claimed to have done what she always does. This really ticks me off. It seems like I find somebody I like and they last about two years before they start screwing up. 

Thanks.

Thanks, Claude! I appreciate your reply.

The toner was probably a lighter level like a level 9 or 10. This past time the toner could have been a 8 or 7 maybe because they didn't have a lighter color and she left it on too long and boom...yer hair turned out too dark. Toner is usually a semi or demi permanent color used to tone down brassiness in the hair and typically you begin to see results after several minutes. That's not to say that sometimes toner takes longer than 1-5 minutes but I have seen cases where it does take longer to knock out that brassiness but very rarely 20 minutes.

Clairol is a terrible color line FYI! I don't think they've changed their color formula since the early 50's when Lucille Ball was the official spokesperson for Clairol.