So, if there are zero per-individual fixed costs from hiring, then it doesn’t matter how many sales any salesperson makes. It seems reasonable to assume that fixed costs are non-zero, so that there is a breakeven below which hiring someone wouldn’t be worthwhile. Here’s some evidence on that which suggests that indeed fixed costs are large.
So, if there are zero per-individual fixed costs from hiring, then it doesn’t matter how many sales any salesperson makes. It seems reasonable to assume that fixed costs are non-zero, so that there is a breakeven below which hiring someone wouldn’t be worthwhile. Here’s some evidence on that which suggests that indeed fixed costs are large.