Rikki, we are both right. You make 1.58% profit of the ally's initial price when they're hired from you. That is the same as 15.4% of the difference in their price before you buy them and after they're bought from you, which is more useful to know when doing volleys.
For example, with a 10k ally, after you buy it, their price multiplies by 1.05 to 10.5k. Then someone buys them off of you, multiplying their price by 1.05 again, raising it to 11,025. The difference in these prices is 11025 - 10000 = 1025. You make 158 profit on this sale.
158 / 1025 = 15.41%