I'm not a veteran, but I do pull about $150 per month from Shutterstock these days. I also stayed at a Holiday Inn Express last night.
I'll throw some pure statistics at you, as it is easier than trying to put it into words.
My best selling Shutterstock image sold like this:
1. 20 sales Week 1
2. 20 sales Week 2
3. 12 sales Week 3
4. 7 sales Week 4
I thought it was dying off, but for the last 2 months, it has reliably delivered 7 to 10 sales per week. So Weeks 3 and 4 seemed to be most telling of its future.
Here's an example of a more modest success, but a steady seller nonetheless:
1. 10 sales Week 1
2. 8 sales Week 2
3. 7 sales Week 3
4. 1 sale Week 4
Despite a lousy week 4, this image fluctuates between 3 and 8 sales per week. It has been doing so for 4 months.
An even slower selling example, yet a slow and steady seller to this day:
1. 17 sales Week 1
2. 4 sales Week 2
3. 4 sales Week 3
4. 4 sales Week 4
For the last 2 months it has been getting 2 to 5 sales per week. It hasn't died, and it maintains its search position. This is an example of not getting too caught up with Week 1. It sure looked promising, but alas it was not meant to be a big seller.
As you can tell, I'm a bit of a stat freak. I track way too much, but I figured it might be useful info to somebody someday.
You won't get rich on sales like these, but if you can slowly build a library of long term steady sellers, Shutterstock can provide some mighty returns.