I assume this is GUAR GUM (although “take back” would imply “gura” rather than “guar” - but near enough I think).
+++++
Hesitate before crossing this teacher (8)
Yes, the ? was meant to indicate it’s not exactly to form.
Traditionally, a ? used in a regular crossword clue indicates it’s a pun.
I think that may be a US thing - in my (UK) experience, a question mark just indicates there is something unusual about the glue, like Oly’s example, or perhaps you need to think laterally. Could be a pun, but not necessarily.
An addendum to my last clue:
Hesitate before crossing this teacher - it sounds like they might take this (8)
Hesitate before crossing this teacher - it sounds like they might take this (8)
Umbrages? (um + “bridges”?)
Not a Harry Potter fan, I take it? You’re so close that I’ll give my intended answer, being UMBRIDGE - a Hogwarts teacher/Ministry of Magic stooge. Probably not a fair clue for a general audience, to be honest. Please do continue.
UMBRIDGES
+++++
Free postage for the Nazi police. (7)
GESTAPO (anagram of POSTAGE)
+++++
Will the apron mutate into a suitcase? (11)
PORTMANTEAU (apron mutate*)
+++++
Smelly French water of German city (3, 2, 7)
EAU DE COLOGNE
+++++
The former Indian Prime Minister: Did he run around with hippies in jackets?(5)
Nehru (double meaning)
+++++
Are you fit or old? (6)
Better version:
Are you fit or crude? (6)
Ack! More apologies.
It was supposed to be:
Are youse fit or crude? (6)
Rustic?
Yes!!
Playing off RUSTIC:
Guevara joins British county to find type of cat. (8)
CHESHIRE (Che + shire)
+++++++
I haven’t been to the fabled isle of Ireland since I was a mere lad. (7)
Emerald (mere lad)
++++
Appropriately in his coffin, Peter showed no emotion (7)
DEADPAN (double definition)
++++
Sketchy medic received terrible performance review after spreading disease.(8)
PANDEMIC (pan + medic)
Sounds like Sherlock’s brother involved his spouse in making corporation. (9)