overpaid or not charging enough?

So i'm relatively new to the whole freelance design thing. I've been just trying to get some clients so i can have a good portfolio as well as a client base to do more work. For the few clients i've had, i have charged much less than what the 'standard' rate would be.

For my past 3 jobs (3 different clients)...all of them have overpaid me on top of the invoiced amount. It's not a whole lot of money that they're overpaying me by, but it still kind of makes me wonder. Each time i recieved an overpayment, i've called to let them know, and they've just said "nope, we did that on purpose...thanks for all the help".

Am i not charging enough for the projects I'm doing? or are they THAT happy with my work they feel that they need to add a little something extra? I just feel like I may be doing something wrong.

Sounds like you are doing something quite right, but I would definitely raise your rates for your next job. :)

thanks rush. :D

LOL! I wouldn't be complaining!

i'm not complaining by any means. It's just a tad confusing. When i recieved the first 'tip' i thought they were just being nice, but then it happened again, at which point i had wondered if they thought i was a charity case. Then it happened again, which made me wonder even more about teh prices i've been charging. So, it's just a general concern for a n00b in teh freelance business ;)