Eric Frank Russell's "Exposure" (short story, alien invasion, free): Bad luck dooms alien invasion of earth

A Rigelian colonial party of shape-shifters has found earth, & early evidence suggests this should be a world easy to take. So they land near a small human camp, take samples of local life, including 2 humans, for dissection, & plant 2 spies each in 4 small towns nearby - spies taking the shape of the two humans they'd picked. How were they to know the specific human samples they had picked will look out of ordinary in pretty much every other city?

Of course, the alien party will never leave earth.

Notes.

1. This is one of the stories with feel good effect, but I found the quick human win in the end too convenient.

Fact sheet.

First published: Astounding, July 1950.
Download full text as part of the scans of Astounding, July 1950.
Rating: B.
Among the stories from Astounding/Analog issues edited by John Campbell.
Related: Stories of Eric Frank Russell (annotated & ranked list - infrequently updated).