Lateral Thinking Puzzles - third time is best!

Were Nancy and Sluggo trying to sell the cat itself?
Or were they having the cat perform some service for customers, while remaining in the custody of Nancy and Sluggo?

No.

See above:
From Saint_Cad:

So a cat meowing made money for Nancy and Sluggo due to the rationing (due to WW2) of a finished object (not raw material) that is not food? Yes

Note the difference.

Let’s trying sidestepping what the item actually is. Were Nancy and Sluggo’s customers paying for the cat to meow? Or to not meow?

No to all.

Neither.

A step even further back: is it accurate to say they have customers?

replacement for a radio?

Specifically a cat’s whisker?

Yes. At least one.

Using this definition for customer from Oxford online:

a person or organization that buys goods or services from a store or business.

Or in this case, from two kids.

Did their customers realize that a cat was involved at all?
If so, did they realize before or after paying their money?

No

Did the cat’s meowing help with advertising somehow?

reply to Thing.Fish:

Did their customers realize that a cat was involved at all? No.
If so, did they realize before or after paying their money?

No.

Does it seem likely that the customers were happy with the deal they got?

.

Yes.

Do not overthink this. This is a simple daily 4-panel strip. (This particular rationing was a theme all week in that comic). The kids see an opportunity created by a rationed item in panel one. Next they ponder how to take advantage of that opportunity while a cat wanders at their feet. In panel three they take the cat (and a blanket) and in panel 4 (meow!) they reap the benefits of their lateral thinking.

Was the cat used as a way to mimic a baby, so the purchasers can obtain an item they would not have been able to get otherwise?

.

No.

Are other people involved in this in any way (even if unwittingly)?
Other animals?

I need to ask better more exploratory questions.