Doesn't seem like a big deal. If someone offers you a very low price just decline. Or better yet, set up a threshold that will auto decline any offer lower than a specific number so you won't even have to respond. Low ball offers will not hamper your ability to get fair market value in any way.
And don't take it personally. For them, it's just a numbers game. They know 95% of their offers will be declined. It's that 5% that do accept for whatever reason that make it worthwhile. I've made quite a few of what I consider to be "low ball" offers (around 40-50% lower than asking). Not that many actually decline. They either make a reasonable counteroffer (what I was shooting for to start with) or flat out accept, which is always a nice surprise.