Cases like yours are so rare, that it is no big deal to offer
to buy them back if the patient doesn't like them.  I do it.

Made one for a guy a couple of weeks ago and he came back to
get his teeth cleaned and said,  "That thing you made for me
really works.  I haven't had a headache since."

Most of them that I make are kind of 'one the side' while other
treatment is going on (I don't want someone to go home and clench
on a 'fresh' root canal, temporary crown, or large filling).
Some of these aren't even charged out, but I know it will help
make the other treatment more comfortable.

Sometimes though, patients just show up for an NTI.  Usually a
close friend or family member has told them their personal story
after hearing this person complain of pain from clenching symptoms.
"Hey, that was me until I got this little bite thingie!"

Steve