In the case where there are requirements that are revealed only after you have accepted the assignment, many (I dare say, "most"
of us consider it entirely okay to promptly ask for the shop to be unassigned when we see unexpected and unwelcome requirements in the details.
The key here is to read the details immediately once the shop is assigned, so that if you must withdraw, the scheduler can reassign the shop and still be able to meet the client's deadlines. It is essential to do this via email, so that you have a record of stating your timing, the reason for withdrawing, and that you expect this to be "without penalty." That way, if a scheduler does not act promptly, you could go back to the project manager if you were unjustly penalized.
If any MSC penalizes a shopper for propmtly declining based on new information, shoppers need to know. This would be the place to report that, if it happened.
You may have been over thinking this, but it is a reasonable and common question for relatively new shoppers. Good for you to have sought advice instead of stewing.
Based in MD, near DC
Shopping from the Carolinas to New York
Have video cam; will travel
Poor customer service? Don't get mad; get video.