I like looking at pet ads online and in the papers. I noticed lately, people are giving away free pets, with a 25 to 50 dollar rehoming fee. If am taking a pet that someone no longer want, shouldn't they pay me?
In many cases, it's not permissible to sell pets, particularly on sites like Craigslist. The "rehoming" fee, or "adoption" fee, is a way of dealing with that prohibition, at least on that site.
A lot of people also call this an "adoption fee". Others look at this re-homing fee as a way to recover some of the costs of shots and getting the pet fixed.
Some people do this as a way to discourage the very casual adoptee acting on impulse, by giving the pet some value, in the thought it will be better cared for. Also it is to discourage those who sell the pets to labs, or dog fighters for example. And, there still those fools unfortunately, who will take free animals to only torture or abuse them.
An acceptable counter, is to offer to pay theasking "rehoming" fee to a local shelter.