Depends. But as a rule of thumb, your host must be able to reply your questions accurately and on time. Because it can involve quite a number of parties here. Imagine if you have a reseller too (if you have a master reseller account) that have a reseller ask his uplink a technical question. This reseller then forward the mail to you. You then have to forward the mail to your host. If they're not able to provide a 5 minute response time then I'd say you have a great chance of getting an angry customer.
Another thing is uptime. Server uptime is abnormal if it falls below 99.89% consistently every month. If it does, I would suggest you to kindly ask your host to swap between servers they currently house. If problem persists then you know what to do.
In business, always look for quality. In this hosting industry, you know as a matter of fact that reselling is enabled. Don't complain about low resource as a startup. Because you must remember, not all customers use all the resources. Customers often have their allocated resources & stay idle in the first few months before they actually starting to use them all. You just have to know what your clients use the resources for to control your overselling flow. Observe and list all things and do it right.
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