Trying to get proof without faking it

I've been running my self-paced Dutch course for about a year and the thing that keeps stopping me from raising the price is that I have nothing to show. Not testimonials exactly, more like evidence that people actually finish and get somewhere. So this month I'm asking every learner who completes module 3 to record a two-minute voice note about where they were when they started. It's awkward to ask and I hate it.