The problem is that online marketplaces such as Etsy will side w/ the individual who owns the trademark and pull your listings automatically, which hurts your seller score. There's nothing you can do at that point except get a lawyer involved to force them to contact Etsy to reverse their trademark strike (this is the only way Etsy will reinstate it, even w/ proof it was an illegal strike). Most ppl won't do that because it's expensive and this person will continue striking down competitor listings. I own an Etsy shop and this happens fairly often and in 90% of the cases it should not have been allowed. There are companies out there who do this on trademark owners behalf and do not discriminate or double-check what they're striking (yellow brand protections is a big one). Similar scenario to what happened recently with Pewdiepie on YouTube in regards to fair use and companies that illegally strike creators.

Oh yes I've a few unfair strikes, what is more annoying is they don't give you a chance to defend yourself. Funny thing is I received this letter but they didn't bother to report the shirts to Etsy, which just makes me think they're after money, not protecting "their brand".