So for a small business owner even 1 person hitting the spam button can be a kiss of death for deliverablity (and I know people irl who think hitting spam and delete are the same thing <facepalm>).
Basically long story short, if you send 100 emails and 10 people open your email and click on something there is a high probability that the remaining 90 are also going in the primary inbox. Otoh if 2 people were to click the spam button then high chances are rest 98 are also going to spam and soon enough you'll be branded as such.
Its why inbox warmup services are so popular nowadays. While I disagree with such practices in theory as most often they are means to abuse filters, your case seems legit and so you may have some luck with that.