This was one thing I was glad for when we moved -- it gave me a chance to set a new precedent, since none of the neighbor kids knew me. It allowed me to be much more hard-assed, right from the get-go, than I had been at our previous house. And you know what? They all (seem to) like me anyway! 
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I have really firm, clear boundaries and am completely unshy about enforcing them, and so far none of the kids have had the slightest problem with it. I just say, "It's not a good time for us to play right now -- come back tomorrow at 10, bye!" Or, if they're already here and I've had enough I just say, "Okay, 10 more minutes and we're going to say goodbye, thanks for coming!" and then stick to it. They really don't mind. Once or twice I've had a kid say, "But whyyyy?" when I've said it's time to go, and I just repeat myself: "It's time for us to say goodbye, see you later!" without offering a specific explanation, because it's none of their business and it would be rude to say, "Because I'm sick of having you here."Â 
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I also have a firm snack policy. I'll put out something like fruit and crackers about an hour after they get here, and once it's gone, that's that. If they ask for more I say, "That was all we had to share -- you can head home and come back after you've eaten if you're still hungry." Or, if it's time for us to eat lunch and I don't have enough for everyone or just don't want to feed everyone I say, "Okay, time for us to eat lunch, see you later!" Again, they really don't mind. (ETA: We cross-posted. That's sad about the kids who truly don't have enough to eat. For them I'd probably offer a sandwich when they came over, but I'd still shoo the other kids away first.)Â
This is great advice. We no longer give snacks. Water only. Sometimes I'll offer fruit or popsicles to DD's close friends. They were eating us out of house and home!
