Ebay goods not as described

wilson1973

I have just purchased a jacket from Ebay,which was used the ad said it was in good condition but with a few small marks that are hardly noticeable,so before I bid I e mailed seller asking for further details of the marks,she said it was a small mark on the inside of the arm and hardly noticeable as the jacket was dark,so I thought ok and bid on the auction and won.
After 11 days when it arrived I was shocked it had stitches coming apart,scuff marks and a small hole on the back and the hole of one arm was covered with heavy permanent dark brown stains as was some of the front and the rear,it would appear that somebody had been using it as a work coat for painting and the stains were very obvious,I was shocked that someone would risk their reputation on Ebay by being so deliberately misleading.
I sent the seller an e mail saying how annoyed I was at the state of it and I couldn't believe they had sold it to me in that condition,they responded by saying
"Please send the coat back to me and I will refund you for the postage costs and the cost of the coat if you do not want it".

The coat cost £10 including postage and it will cost me £4 to return I'm not sure if they mean they will refund the return postage cost or the initial postage cost and then the value of coat.
I don't like giving bad feedback,and their feedback had been good before this major oversight,so could anyone advise me as to how I follow this up should I just post it back to them and not involve Ebay and have I got a right to have the return postage paid,I would prefer to do it in a way that doesn't blemish their record on Ebay