You have several tools.
The first is educating the seller as described above. Some sellers, especially newbies, don't realize their advertised price is set in stone.
Second is asking for a Mutual Cancellation. This ends the transaction amicably, gives the seller his fees back (which can amount to 15-20% of your payment). and allows both of you to leave feedback.
If the seller files an Unpaid Item Dispute instead, you can win it by paying the original advertised amount.
You have up to 60 days to leave appropriate feedback. The most effective feedback is calm and factual.
At the same time you can leave Detailed Seller Ratings. The normal transaction gets 5 stars. The lowest Rating is ONE.
And remember you catch more flies with honey than with vinegar.
