I post stuff on CL all the time. Lowball offers are part of the process. If it's too low to counter, I ignore it. If it's low but in the ballpark of where I want to end up, I counter wit my bottom line price, take it or leave it. No reason to take any of it personally. And I don't see where sending somebody a lowball offer, whether it's a straight sale or trade plus cash, is insulting to the seller or trying to "take advantage" of the situation. Seller can ignore or say no thanks and move on. But you never know what might work unless you ask.