I still wonder about the proportion of people accepted in each of those categories. I have to think that the percentage of people you accept as clients that you knew previously is way, way higher than the percent of people you accept through queries.
The percentage on signing someone from slush is certainly much, MUCH lower (it's been quite some time since I have run percentages, but at one point I found I was requesting about 7% of my queries, and from the fulls I'd requested, offering on maybe 5%. . . meaning about one-third of 1 percent, or 0.35%
That said, it's as much about VOLUME as anything. If I offered on even 1% of everything queried to me, I would sign a new client every single week. And by the end of the year be so overwhelmed I'd close completely.
We remain selective because it's the only way we can be effective. If we have too many clients, steam comes out our ears and our laptops explode.
So basically the low offer-rate on slush isn't just about your writing being good enough, it's about our lists not being too big.