There are so many scammers out there it is hard to find good lobbies. If you would like to find a legit lobby and not get scammed nor help a scammer follow a few simple instructions.

For Rep Lobbies:
Most rep lobbies are scams. A rep lobby should have an invite first and rep later. If the person is legit, give them rep after the match. Many "hosters" would say this wouldnt work because they wouldnt get rep and the people would scam them. If someone is Legit they will get rep for hosting a lobby and asking for rep AFTER the lobby.

For Money/MSP Lobbies:
Many of these are scams too. MSP lobbies are easier to get scammed in because there is no dispute after the lobby. Paypal is harder to get scammed in because you can report a scam. Always look for a LIVE stream, youtube can be deceiving, because many peopleupload a video they downloaded from youtube. If you look around you will see the majority of "lobbies" and the "proof" are usually the same videos from person to person. I have seen almost 100 youtube videos claiming a free lobby but I only saw three videos. (in other words all the videos were just the same video posted by different people looking for subs, MSP, and easy money.

Headshot Lobbies:
These are NEVER legit because if someone realy has a lobby they can get like 500 headshots per kill, so why would they need headshots if they are always hosting free lobbies?

As a good rule of thumb anybody you meet on xbox live should show you one prestige before you ever have to pay a cent. Maybe you will pass up a legit lobby but there is a greater chance you are just going to get scammed out of your (or your mom and dad's) hard earned cash!