The easiest pitch would be to have a base retainer (say 1000$ a month) and then % of revenue increase since the baseline.

It makes it easy for them and is far compelling cause you are now a revenue cost rather than a recurring sunk cost.

The typical ecomm transaction has 10-12% margins? And then CAC etc has to be amortized. So you'll either have to pitch fora tiny sliver of topline or a % of profits - as that also aligns outcomes where the consultant just doesnt run promotions giving away all the margins and think short term.

Given this math, id say 10K a month revenue seems a bit early. Might want to look at ecomm stores that are a bit further along the way, or use pre-recorded content on subscription to tackle this early market (as it potentially) can become your funnel.