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Well, as I said I think a theme is covered by the GPL and that the developer cannot demand anything more than that the original credits are left intact - these could be in the code comments - restricting the use of the software is against the GPL.
However, if a theme is really good, I feel it is not good tone to remove the link AND not pay a voluntary donation to the thememaker. There's a big difference between voluntary and forced, though.
Regarding work: I don't charge for a quote. On larger projects I charge for a requirements specification, but that's only to be paid if the client chooses another developer for the actual work. It's my policy that there has to be some kind of benefit for the customer before any payment, so just charging for the act of giving a quote is not fair, I feel, unless I in the process make a product for the client. This product could be a structured requirements specification, with which the client can go elsewhere.