How do deal with lowball rude offers?

I have this antique washer that is in great working condition. I listed it at $400 and I KID YOU NOT this is a message I received:

“I can offer $50.00 not worth much more anymore couple years ago yes but since you’re not sure if it works $50.00 is the highest I can offer this machine is from 1930-1940 era”

I looked around and a lot of others are in the same range and even found a few up to $600. Should I even respond? Why would someone think it’s okay to be that ignorant….?