If a quiz says unlimited submissions on avenue then every time I submit will it take the highest mark?

Like say for example the first time I submit I get 17/18. Then I answer the question I got wrong with the correct answer.... then will I get 18/18? Or will I get the average of two quiz marks...???

If it has unlimited submissions, then you can submit it as many times as you can and they will take the highest mark, not the average...to be sure, i would just ask the prof/tas.
Also, note that if you repeat a quiz again, most likely you are not gonna get the same quiz the 2nd time around, you might get a different quiz!

this is for commerce 1pa0 thoughhhhh

well if it is worth 0 credits, it is likely a pass or fail course, so as you should be fine.

But I do agree that it may be a different quiz, but it can't hurt to take a look at the other quiz since it isn't worth anything