Emails sent via EmailOctopus rely upon Amazon as the ESP (email service provider) to monitor and control the variables of spam.
Regarding complaint rates, there is not a "definite" figure which will result in a ban from EmailOctopus and Amazon SES. Generally speaking though, try to keep these around 0.1% or below for your campaigns.
Use the below equation to calculate if your complaint rate is below 0.1%
If you'd like to familiarise yourself more about how AWS handles complaints read here: