Sewing, Sergers, I'm sorry for the text only post!!

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So my sewing machine junks out on me too much. I know it's time to start looking for a new machine. But, I also know that I want my seams to look better on what it is I make, seeing as I hope to sell my shirts and tunics in a brick and mortar store. Here's the question to the many crafters out there that I know are more experienced in the field than I am; whats the deal with sergers? I've never used one before. Complicated? Cost? What can/can I not use it for?