No one is safe from spam complaints. Complaints can happen even to good marketers who are sending to permission-based email lists.
The complaint rate used to be underestimated, but the recent research shows that 20% of deliverability issues were caused by a lot of spam complaints.
The complaint rate is calculated as the number of "report spam/junk" complaints out of emails sent. For example, the 0.1% complaint rate is considered acceptable and often seen among good senders, but the 0.5% rate is already too high.
While you may not be able to achieve zero complaints, you absolutely can reduce and maintain your complaint rate at the acceptable level to increase your Inbox placements.