Technically reselling is not illegal. It is what most shops do - buy plastic thing in a plastic bag and sell it to someone else.
Of course, tho in Services and Creative, esp those that thrive on Credit for work done, not letting the Creative know what the work is for is un-professional in the extreme. Most real professional will decline the job instantly. I pretty well do.
Reselling under another name is actually depriving the real creator of their moral right to be acknowledged (law in most civilized countries as it is a pillar of IP law).
If reseller doesn’t acknowledge who they are, why they are there, and what the work will be used for, I think they are at least a very poor person to be working with.
In this case, probably nothing you can do but make yourself less attractive to bottom-feeders and more attractive to real buyers who will honor your work.