Forgive me if this has been mentioned before, but I am currently on a writers' loop where several members have mentioned receiving their SASEs from an agent(s) with their rejection written ON the envelope: "Not right for us." That's it. Nothing INSIDE the envelope.
How tacky is that and how much more time would it have taken to print out a form rejection, stick it in the envelope and retain their reputation? Is this a common practice?
I hope not, but in all fairness, you have no idea if the envelope arrived sealed. You think that sounds stupid? I get at least one a week that is already sealed cause it got wet in transit.
This falls into the category of laugh and move on.
There are a lot of agents in the world. Query widely.