hiring a contractor tips

[Kevin Marcucio]

so i have a porch that is sagging and causing the top porch and attic above it to sag too.  the beam post is starting to pop out wards away from the house where the house number 8 is.  so a guy said his friend is a licensed contractor who can fix this for 5000.  he wants 3000 up front lol. and also to get a building permit. so i have a couple of questions. 

1.  how do i know if he is a licensed contractor?

2.  how do I protect myself from him just taking my money and not doing the job?