Been running my own mail for a long time, and with one big exception[1] and occasionally spotting misconfigured systems, any time I've had delivery trouble it has been my fault.
If someone is bouncing you, make sure your ducks are in a row. One easy thing to do that won't catch everything but will help is to send mail to a Spamassassin-protected account, and look at how it classifies things.
[1] The Deathstar has been bouncing me for a long time, and their postmaster appears to be /dev/null. Given that I've had exactly one person using them I wanted to mail, they can bite me.
Except sometimes, like when Comcast looks at your DMARC policy that specifically says "p=none" and decides that means "reject all mail from this domain". Gotta love those guys.
Edit: s/spf/DMARC
Then I discovered my provider didn't set up SPF and DKIM correctly so emails were failing authentication.
There are many factors affecting email delivery beyond SPF and DKIM, and it can be difficult for a small provider to get everything right.
So if you're having delivery issues I'd start with that, not by assuming without evidence that the big guys are intentionally classifying spam just because it's from a small provider.