Level 21 (215 slicing) with over 100k credits due to slicing. Each mission costs ~1k with 15 minutes or less to complete, normally return is ~2k+, highest I've seen is 3k profit. I run both my companions on slicing missions whenever possible.
I've failed less than 5 missions and that is when I didn't really notice the yield rates/mission colors (would just randomly click one and go).
To me it seems like other professions would be making money just as easy since they could sell their materials/created items for an inflated amount due to how much credits slicers have, but this is just speculation.
People who are stating they aren't making money, barely break even, and/or constantly failing must be doing something wrong. My brother who went the the nonslicing route has around 25k credits and is the same level as me. Does slicing need a nerf? Maybe, but I would rather see improvements made to the GTN to make selling crafted items/materials easier and maybe some improvements made to other crew missions.
buffs not nerfs!