Keep getting lowball offers from same buyer

I’m a very part time seller, and I have an item listed for $600. Every week the same person offers me an amount, $50 more than the week prior. I always counter them with $500, but they’ve never come up past $350 to date. Is this someone you’d block? I’ve never had to block someone in the past but I’ve been reading this subreddit and see a lot of you recommend blocking!