Okay, if you already have a certificate, then I think your "reputation" is too low. And the IP address of the host server might be another thing (listed on "blacklists"?).
One possible solution (I do
not recommend it because certificates are a money making machine) might be an Extended Validation (EV) certificate. This gives your certificate "Instant customer confidence".
BTW, even renaming your files would not help, because anti-spyware / anti-virus products analyze downloaded files to detect its binary contents.
Friedrich