When you start thinking that 60-grit sandpaper isn’t coarse enough, maybe that hand plane wasn’t such a bargain after all.
Seriously, I can understand not factory-polishing the sole until it’s mirror-bright, but when you don’t even machine it to be vaguely flat near the mouth, I think you’ve cut costs just a bit too much.
[Update: after more than half an hour (plus cooling time) on the belt sander with an 80-grit belt, it’s almost completely flat. Unfortunately, the last of the deep factory-supplied scratches are just in front of the mouth, so it needs a little more work. So, yeah, cheap planes are no bargain; the Chinese manufacturer put a brushed finish on the sole to hide their poor machining.
Also, while I’m on the subject, Spyderco’s ceramic bench stones aren’t even close to flat. I bought them a long time ago and was never really satisfied with the results, but I’d just assumed that they shipped in decent condition. Nope; I pulled them out while I was working on the plane, checked for daylight with my engineer’s square, and started lapping them on a DMT Extra-Coarse diamond stone. It takes a lot of work to clean them up.]