This ain't none of my goddam business... but my 2 mao are that I stand with our friend, No Friend, on this one. If the original poster actually likes her kitten and people offer to take it in, they are actually doing her a favor and shouldn't have to pay for it. If, on the other hand, the kitten is generally seen as just another object to be sold, well then I guess I'm the one making a mistake.
To stretch this to its hyperbolic limits, can you imagine someone saying to you: 'I unexpectedly have to dash out for a couple hours, can you please do me a favor and watch my kid? By the way, he's a really cute kid and costs me one hell a lot of a money that I would like to recoup, so you'll have to pay me 1000 RMB an hour for the privilege.'