Upload & Sell: Off
It looks like you posted a 100% crop of the first surfer (good). If I look at it at 200% I can see the vertical lines but they seem to be compression artifacts from the 8x8 JPEG blocks, due to the low level of quality in the JPEG saving.
When you see the vertical lines, are you viewing the Raw in your converter before saving the converted image or are you looking at a JPEG you saved and have opened to look at? Try saving at high quality (11 out of 12, or 12 out of 12 in Photoshop, or 95 % to 100% quality index).