I just curious there are some neighbor website with bad reputation (low rank, spammy, dangerous, etc). How big that issue can impact my website reputation? Any solution to fix this issue?
The area most commonly mentioned regarding IP reputation is email. For that, you can let email servers authenticate that your emails are actually coming from your domains, by using such tools as DKIM, SPF, and DMARC.
My understanding is that search engines will not bother with server IP addresses as far as SEO goes.
I think you may benefit from setting these policies properly. You’d need to check with your mail provider (often the hosting provider, but sometimes not) for help with setting these records, as each may ask for different settings. Once you have the instructions, then you head to Cloudflare dashboard > DNS tab and add the records accordingly.