Though you feel a little guilt looking at them, it's the feeling that you're being fooled which is very irritating. Tonight the guy was limping a bit, 2 years ago he was begging at the car park with a cast on his elbow and after an hour you see him walking without the cast. Just pay your Zakat to the Zakat fund if you don't know any valid recipient and rest assured that it goes to where it really needs to be.