Domain Squatter sent name without payment

Ok so obviously I am doing this from a throwaway account in order to not be thrown under the bus entirely here but i have an ethics question for you guys.

I found a domain name I really wanted for a webapp I am building and emailed the woman only to confirm that she squats on domains for a living.

She was originally asking $500 more than I could buy it directly from godaddy for (obviously she already had it for sell through them)

so I threw around the words alexa page rank and search term frequency and did my own "valuation" telling her the name was worth much less ... she agreed to sell it for a much lower price and sent me her paypal address then preceded to transfer the name through godaddy BEFORE i ever paid her.

so what does moral obligation say here? my gut says pay the lady but the part of me that hates squatters thinks it may be worth it not to

So whats the verdict?