Do buyers ever sue the seller for selling them $100-300 fake as authentic?

I wouldnt sue. I would follow the steps (contacting seller, disputing, Etc) like anyone would tell you here IMMIEDIATELY upon receiving it.

Unfortunately, I think you may be a little too late to take those steps.

But sue? No. There is nothing I would buy on eBay that would ever be worth suing.
 
I would in a heart beat! I all but had the civil complaint filed in the Superior Court for Middlesex County in MA on the 'yellow bag fiasco". I am a practicing attorney in NJ and MA so for me, I have no problems telling a seller exactly what course of action I will take. The seller on the yellow bbag would not give back my $1000 which is alot! I was not about to sit back and do nothing. It would have cost me meager duckets to file the claim and haul her a*s to court. Costs her wayyyy more to hire counsel than to refund my money. Even the threat of a lawsuit seems to get people singing a different tune and FAST. Moreover, in an effort to help others who have been scammed on Ebay, I offered free legal help (i.e., I would write a letter from my firm on their behalf) to help them get their money back. I have no problems helping out a fellow tPF member free of charge!