I have done over 1,100 transactions on eBay. I had 1 negative in all those transactions. I sold an auto book and was never paid for. When I left negative feedback on a sale gone bad, the buyer left me my one and only negative. That is not how feedback is suppose to work.
However in this case, If you bought a product and were not happy with it the first thing you do is contact the seller. They might of said send it back and I will refund your money. In that case once complete you would of left feedback such as "Customer stands behind transaction" and left a positive feedback. After all whether some thing is worth $40. is opinion but they in that case would of left you no worse off so you were made whole. Now if you contacted them and they said pound salt, then you could of left the feedback you did.
Without sounding condescending (I don't mean to be) experienced eBayer's always hold there breath when dealing with someone with a rating under 50. They sometimes just don't understand the feedback rating system and can be a hair trigger. Negative feedback should not be left unless you've made an attempt to first contact the other member. As you go to leave anything but positive an eBay warning appears on the screen stating that. Your Dad should of followed the eBay warning "If you have a dispute, contact your trading partner to try and resolve the dispute before leaving feedback."