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human
[Harry Potter] Wait, was Snape the ONLY spy within the Death Eaters?

Seems odd that Dumbledore would only have Snape as a spy within the Death Eaters. 

What if something unfortunate had happened to his only spy? Wouldn't it be smarter to have at least a few double agents, each at differing ranks, to have infiltrated the Death Eaters?
gpt
You don't just walk up to Voldemort and say you wanna be a Death Eater. They are only very few in the Order that could even try. Quite a lot of them aren't pureblood or are blood traitors like the Weasleys so they would probably be killed/tortured on sight.

And for those that would qualify it just is an insane risk. If you aren't an expert in Occlumency you will be caught fairly soon. So the only proper way to get someone on the inside is to turn them. Snape was pretty much pure luck for Dumbledore and most of the other Death Eaters are way too insane to even attempt talking to them.

And there is always the risk of them being exposed and getting Imperiused. Suddenly there is a double agent in your ranks, not fun.