If you run an agency business model from which you earn a commission e.g Uber, should you value your business using GMV and what are the average valuation GMV multiples?
The valuation of your business depends on your ability to make a profit and your rate of growth. At one extreme end, a business with a very high rate of growth (%20) a month, can get away with no profits as in the world of startups.
On the other end, a business that is making a profit, with %0 year of year growth is not investable so is valued very low.
The other thing, I don't think it is fair to look at Uber as an "agency model". This way of thinking would be to miss the point on where & how they create value and thus are valued commercially.