New to Craigslist, question about dog\cat\puppy\kitten posts

Portland OR

Description

I'm looking for a great dog and\or cat. There is something that confounds me though: Why don't people with animals post the cost of the rehoming fee in their posts? Are they trying to get as much $$$ as they can for their animals? Does their fee change over time? It seems that failure to do this just leads to unnecessary texting and emailing back and forth. It has a smoke and mirrors vibe about it. I ask because I legitimately want to understand. Thanks