I do agree with you, The same thing happened with me as well. I have sold plenty of ab king pro benches, in context of which i have got positive feedback but couple of days back i got negative feedback from the buyer just because she could not understand the contents of the bill and left feedback in hurry.
Another customer bought same item and left negative feedback as he explained parts were missing and pad was torn. As i have already mentioned in the listing that please check the courier in front of courier man, if find damaged then do not accept it. I am incurring huge expenses on packaging and using finest courier services of india besides keeping low margin of profit. You really get hurt when you get these kind of responses from customers without having any of your fault.
customers do not accept their fault and leaves negative feedback without contacting the seller.
mostly I have seen, People who picks up the phone and says item ok do not leave feedback and who do not picks up the phone leaves negative feedback.
Customer who left the negative feedback gave me wrong number and i mailed him many time but he is unresponsive.
yes, you said right, sometime it feels that your competetor is doing the same but one thing remember he can not be the god for you. if you are supposed to get success you will get it.
Negative feedback does not mean it can stop you, it will bring new experiance in your way.
Remember: A man who wants to acheive his aim must not care the obstructions on his way.
Apply in the community court, Explian them each and everything. it will take some time but everything will be all right.
Try to put the pictures as evidence. Total you can upload 3 pictures
make then understand you sent him the same stuff of t-shirt which you have sent to other.
Wish you good luck.