Tips:
Look on topics with vouches and livestreams. If they have both, read the vouches, and watch the live stream. If they look real, it most likely is.

Check to see if they're online, if they're constantly playing the same map (when you're look at they're profile), usually rust or afghan, it most likely will be a lobby.

Ask them stupid questions if you are paying, but make it sound smart. For example, ask something like "Do you have an m9 hash within the Jtag?". This is a trick question, if they answer "Yes." then they obviously failed. Be creative with this one.

Look for Gold members that host. They normally would not fake it, since they payed for gold and obviously don't want to loose it.

Pay close attention to the "proof" they may have. It most likely might be made by someone else, so always watch for this.

Click on their profile and look at recent posts. Look for suspicious activity, such as posting for an invite on another thread.

Warnings

Watch for the topics that the person who makes them wants to spam a gamertag with messages. These are sometimes very obvious, as the posts are normally very brief.

Try to avoid paying. NEVER pay with microsoft points or Xbox gold. Only do paypal payments if you are 100% sure.

Be careful of deranking lobbies. They are normally too good to be true, and then they derank you.

Watch for accounts that are newly made. If they just posted their new topic, and it's their first post, be suspicious.

Some people like posting topics with a gamertag, but don't invite anyone. These are quite common; however, they still might be legit, only patience will tell.

Read the vouches carefully, look at their accounts and make sure they aren't fake accounts for the topic owner's bidding.

I do hope you like this post, and find it informative. Always watch for these things so 2 very important things don't go to waste: Time and money.