Hi,
I know this topic been there few times but I find it still bit struggle to figure out. I’m freelance web developer and I offer managed services and Cloudflare is no-brainer for DNS/CDN/WAF usage. But according terms for the self-serving services I cannot sell, resell etc. and there was some incident somebody having thousands of domains for clients under one account.
As I mentioned I’m now freelancer and with rather few clients I’m definitely not suitable for Cloudflare Partners program. Also my clients expect to point domain and let me handle everything else for them.
From discussions I read it seem to be best to make separate account for each client and manage it from my account. I like that also because when they decide to get somebody else it’s separate and not stuck in my account. Shloud be fine with terms as I literally manage their account for them (I would be fully transparent that we are using CF, if their are ok with it etc.).
This concept is fine for the free accounts, but what about paid plans? As I mentioned they expect me to handle all the things (hosting, dns, services…) and pay me for that in one invoice. Need of credit card/Paypal would definitely prevent many to switch to paid plan. Only way would be to put my billing information and card into another account to handle that part. And there I’m definitely not sure if it’s ok or it would be problem if I would be paying in few separate account. 
I just want to my clients use Cloudflare and even paid plans, but also in proper (legal) way, where I can manage everything for them. Thanks for any help or tips.