A Traffic exchange core feature is the ability to rotate urls and understand the basic rules of rotation will allow you to work out why members are not receiving as much hits as others.

Basic Rotation Rules

1) The URL is not banned - If url is banned it is in "Not Approved Status".
2) The URL is not paused - If the url is paused the member who added it checked the pause box.
3) The URL owner is not banned - If the member is banned their sites will not display.
4) The URL owner is verified - If the member has changed email address he becomes unverified.
5) The URL owner is active - If they are not active they will receive no hits.
6) The URL owner has hits - They need hits in their account for their urls to use.
7) They DO NOT see their own URLS - It would be pointless looking at your own urls.

These are the main rules urls need to pass before they make it into the advanced rule set which picks one url from all the others, Since 2.1 you can change this rule set for random or last hit.

Random Rule Set

It takes all the urls that pass the basic tests and picks one from random, It works like having your name in a hat with a few others the more your name is in there the greater chance you have to be picked, But if you get picked to much you will run out of hits making them need to surf more. The flow can be very uneven it can change day by day even if your surfing count doesn't.

Last Hit Rule Set

This is the fairest of hit distribution a URL will not get 2 hits until all the other urls have received a hit this makes the flow of hits to urls even every day until your surfing count changes. This can make it appear slower than it really is.

The downside with this rule is if someone adds the same url 10 times right after each other when it comes to them getting their hits the person viewing them may see the same one 2,3,5,8,10 times in a row depending on the current amount of surfers.

Both of these rules do work very well, It changes between exchanges by their member database for which final rule is correct. The best way would be to try them each for a period of time and compare the outcome.