Earnest money

I’m selling my MIL’s house as she had to go into assisted care. The house is listed at $450k. We got an offer yesterday at list, they’re paying closing, we’re paying both agents (which we’re ok with), and they are putting 35% down but they want to only put down $500 earnest money. To me it makes it sound like they’re not serious. I’ve bought and sold a few houses but I’ve never heard of such a small amount of earnest money. I’d appreciate the opinion from someone with more R/E experience.

UPDATE: the other party signed our counteroffer!!