/biz/ - Business & Finance

Can I get in trouble for going to various currency exchanges and make a buck off of the varying value of the dollar?
I recently got into buttcoins, and I've found one marketplace that allows free deposits from debit cards and free transfers, and strangely always have the BTC exchange rate a few dollars higher than any other marketplace. So I thought it would be fun to see if penny day trades would work, and sure enough I made a couple cents from a few bucks by depositing USD into a market with no deposit fees, transfer the USD to another market that would automatically convert the USD to their (much lower) BTC value, and then transfer it back to the first one with no fees and high BTC value, revert the BTC back into USD, and marvel at my tiny success.
I've done the math, and made it a bit more conservative just in case, but it still seems to check out. As outlined in the image, I should be able to have a decent profit from my endeavors.

Anybody have any thoughts on this, like something glaringly obvious that I should be ashamed for missing? Also, legality. It doesn't feel legal to make money like this. Taxes will be paid, of course, but I am unaware of anything else that might sting me.