"Should it not tell me before I part with cash, maybe even tell me on the market page?"
Yes it should. Either in the readme or the product page.

Plus the licensing/useage terms shouldn't offer any additional restrictions over the store licence, unless these are there for a good reason. And pre-agreed with the store beforehand.

A good readme for freestuff or products should state clearly if there any restrictions, and it should also offer some 'protection' for the vendor and freedom for the artist. 

Overall though I reckon most are pretty fair and reasonable. Normally If theres a useage query most vendors are cool about it if you ask nicely. 

Pinky - you left the lens cap of your mind on again.