Reporting part-time earnings while on benefits - any advice?

I work some days through a staffing agency while still certifying. I would rather hear the honest version than the polite one. The form asks for gross earnings, which I do not see until later. Who can I ask without risking my claim?

Thanks for writing this out. I went through something close to it 6 months ago, and it settled down once I kept a simple log of every call and form.