Datacenter IP is the first thing most teams block on, and on its own it is a terrible reason to refuse anyone.
It tells you the request did not come from a phone or home broadband — it came from a rented server. That is genuinely useful information. It is just not a verdict, because the population it catches is mostly VPN users, and VPN users are disproportionately the security-conscious, privacy-aware, technically-literate people you would quite like as customers.
Same for disposable email domains: often it is someone protecting their inbox from a product they have not decided to trust yet. Same for a freshly registered domain: sometimes it is a founder who launched last week and is signing up for tools.
Each of those in isolation is a reason to look closer. None is a reason to refuse.
Where it becomes unambiguous is combination. A disposable address, from a datacenter address, on a domain registered yesterday, as the fortieth signup from that subnet this hour — nobody is arguing that is a customer having a bad day.
