In this case, you'll have to rely solely on the Browser trust model. Here's a couple reasons why.
CloudFlare as Proxy
CloudFlare operates by acting as a TLS-terminating proxy. That is - you connect to CloudFlare, and they connect to whatever server their customer has configured to fetch the page. Your TLS session is with CloudFlare, and they may or may not have a separate session with the origin server.
Since CloudFlare is the termination for your TLS connection, whether you like it or not you'll need to trust CloudFlare to use this service. The connection maintains no trace of what was on the back-end connection of the proxy except for the page contents of the result.
Here's the part I don't like about CloudFlare personally: since CloudFlare provides an option for customers to operate without TLS on the backend, you effectively have no assurances when connecting to CloudFlare that this connection was encrypted between CloudFlare and the origin server.
On the flip side - one could argue that it's not CloudFlare's responsibility to secure the connection to the origin if the customer has chosen to use insecure settings.
CloudFlare as Certificate Authority
The certificate is issued to CloudFlare, and they manage the Private Key for their proxy servers. So if you want to use this website, you'll need to trust that CloudFlare is not going to allow the compromise of one of their customers' websites by issuing certificates for a domain they have not validated to be controlled by their customer/user.
The protections against them issuing false certificates are partly technical - as there are watchdog organizations that run crawlers looking for rogue CAs, and we also have Certificate Transparency Logs which can be monitored by domain owners to see if a CA they don't work with has issued a certificate on their domain.
But the main protection against this misbehaviour from CloudFlare is human. The CA/Browser Forum is a collaboration between Certificate Authorities and Browser vendors to set some baseline rules for who is allowed to have a Root Certificate included in the Browser's trust store. If CA's are found to be issuing rogue certificates - or are otherwise in breach of industry best practices - the Browsers may punish them by revoking their status as a trusted CA.