Switching flavors requires a carto change? Can they be cleaned or at ~2.00 a piece should you just replace them?
Some folk claim you can clean a carto, but those people are just not right in the head

Not only do you need to replace the carto when you change flavors, you should also give the tank a good wash. Some flavors can "stick" around longer than others. Strong cinnamon or licorice are problematic.
The MOST important thing you need to learn is how to properly prime a carto. If you do not prime them correctly, you will not enjoy them.
Here again is Baditude's Blog. Read it. 5 times. Not 4. http://www.e-cigarette-forum.com/forum/blogs/baditude/3710-5-baditudes-cartomizer-tank-setup-guide.html
Then go to youtube and search for priming cartomisers. Watch at least a Dozen different ones, 3 times each. Then pick the method that makes the most sense to you, and do it that way. You will mess it up at first. You will spill much eliquid. Then, you will get it right and you will have a great vape.