I've never really communicated this before because I'm not a stickler for rules because there aren't really any rules but if someone asks for more than one or two newer games when I update the list I may limit how many I give that person at once just so nobody swoops in and claims them all before other people get a chance to look. When people ask for more than a couple of games that have been on my list for a while then I usually give them all of them.
I assume people that ask for the games will play them maybe not right away but at least some time in the near future. I don't expect anyone to play them to completion or anything but that everything is done in good faith and nobody is just stacking games in their Steam libraries to collect e-dust. I even give people games to give to their friends because I really don't care as long as someone plays them.
That said, people who offer to review or to share their experiences usually get preferential treatment when multiple people request the same game but otherwise it's first come, first served.