Are rejections eating you alive?  Do they shake your confidence, or are they immediately forgotten like what you had for dinner last night?  Chances are, the longer you sell microstock, the less rejections will bother you.  

1.  Don't take rejection so damn serious.  Rejections happen.  An editor doesn't care if this is the first photo you've ever submitted or if you are a famous portrait artist with canvases hanging in the National Art Gallery.  They rejected the photo, not you.

2.  Shake it off.  If you feel the hair start to raise on your neck each time you think about a specific rejection, it's time to  go for a walk to the fridge or the corner pub.  Nothing personal.  But..... what if you are right?  If the editor clearly has bad taste or if there is a chance he just got dumped by his girlfriend and is taking it out on you, don't kick your dog.  Put the photo aside for a few days and reevaluate.  Ask yourself if your attachment to this photo is personal or if you believe in your heart of hearts that it has potential to rock the design world.  Is it worth a resubmit to sell a couple times?

3.  If the agency says the photo has limited commercial value, it has limited commercial value.  Trust them on this.  Once a distributor has a few million photographs in their collection they get pretty good at judging these things. 

4.  Learn from it!  Most rejections contain valuable advice that will help you improve as an artist.  It's becoming a cliché, but ask any experienced microstocker and they will tell you that they have learned soooo much from their rejections.

5.  Calibrate your monitor.  Do it now, and every week at the same time.  I can still remember my horror when I saw some early non-calibrated work on another monitor.  My perfect background was full of streaks and pen strokes.  In my case, the editor on duty couldn't have calibrated their monitor either and I was fantastically fortunate that the photos were approved.  Or was I?

6.  Know your place - but don't be restricted by it.  A niche is a good thing, but eventually it may lead to your demise.  Are you responsible for that "overabundant category" refusal?  Have you become direct competition to yourself?  It's wise to be a master of a specific topic, but you are not betraying anyone if you stray over to new subject now and again.  Might even spice up your approach to your niche.

Sure, once you have an agency all figured out they sometimes hire new and ruthless editors who cause masses of contributors to moan and complain.  Historically proven, those new editors should loosen up a little bit but more surely you will find yourself adapting to the new rules.  Like the man who must untangle the Christmas lights, maybe it's how we stock photographers handle our rejection that sets us apart.