Most reseller support requests are a small number of problems in rotation. Once you recognise them, the majority take under five minutes; the time goes into the ones where the symptom points somewhere other than the cause. This is a diagnostic list instead of a list of fixes, ordered roughly by how often each one arrives.
"Several things broke at once"
A client reports that email stopped arriving, the contact form fails, and they cannot stay logged in. Three unrelated faults in one message almost always means one cause: the account is at its disk quota and cannot write anything.
Check Show Accounts Over Quota in WHM before investigating anything else. It takes ten seconds and resolves a surprising share of tickets outright.
When it is full, find out where the space went before raising the limit. Open the account's cPanel from List Accounts (no password needed) and look at disk usage by directory. It is usually a backup plugin that has been writing into the account for two years. Deleting those fixes it permanently; raising the quota just moves the same conversation to next month. Managing customer resources walks through the pattern.
"My site is showing someone else's page"
Nearly always DNS. The domain is resolving to the server's shared address without being correctly bound to the account, so the server answers with whatever is at that address by default.
Check that the domain's nameservers actually point at yours, and that the account holds the domain. If the client changed nameservers in the last day or two, some of the world still has the old answer cached and it will resolve itself.
"The site is not loading at all" after a domain change
DNS propagation, in the overwhelming majority of cases. The client changed nameservers an hour ago and is refreshing.
Confirm it rather than assuming. Look up the domain's nameservers yourself; if they still show the old provider, nothing on your side is wrong and it needs time. If they show yours and the site still does not load, the problem is on the server and worth investigating.
Lowering the time-to-live on DNS records a day before a planned move shortens this window considerably. It is worth telling clients before a migration rather than explaining afterwards.
"Email stopped working"
Three causes, in order of frequency.
The account is at its disk quota, so nothing can be delivered. Check that first: same as above.
The mailbox itself is full while the account is not. cPanel sets a per-mailbox quota separately, and a mailbox that has been collecting everything since 2019 hits it eventually.
Or outgoing mail is being rejected by the receiving side because SPF and DKIM are not set for the domain. This shows up as mail from the site landing in spam or bouncing, and it becomes visible right after a migration because the previous host had those records configured.
"I cannot log into cPanel"
Confirm which panel they mean. Clients say cPanel for everything including WHM, webmail and WordPress admin.
If it is genuinely cPanel: check the account is not suspended, then reset the password from WHM rather than trying to work out what they typed. Repeated failed attempts also trigger a block on their address, in which case waiting or clearing the block is the fix.
You never need their password to look at anything, so do not ask for it. Open their cPanel from WHM's List Accounts. A client trained to send you passwords is a client who will eventually send one to someone impersonating you.
"The site was working yesterday"
Ask what changed, and expect the answer to be nothing. Then check three things: whether an update ran, whether the account went over quota, and whether the domain or SSL expired.
Certificate expiry produces a browser warning that clients describe as the site being down, and it is one of the fastest fixes available once you recognise the description.
"I am out of accounts"
You have used every cPanel slot on your reseller plan. Suspended accounts still occupy a slot, so suspending clients does not free capacity: only terminating does.
Go through the suspended list and deal with genuinely dead accounts properly, with backups, rather than deleting whichever looks oldest. Terminating client accounts goes over the checklist. If everything is live, the plan is the constraint instead of the housekeeping.
"A client's site is sending spam"
Suspend it immediately, before working out what happened. The account is yours, the reputation consequences land on you, and every minute it continues makes them worse.
Suspension preserves the evidence, which termination would destroy along with the problem. Then investigate: it is almost always an outdated plugin on an unmaintained site instead of the client doing anything deliberate.
Restore from a backup taken before the compromise rather than cleaning injected files by hand, and make sure everything is updated before the site goes back online. Otherwise the same automated scan finds the same unpatched plugin within days.
"Provisioning stopped working"
If accounts stopped creating automatically after you tidied your packages, the mapping in your billing software points at a package name that no longer exists. WHM has no rename, so changing a package name is a delete and a create as far as anything referencing it is concerned.
Re-check the product-to-package mapping. Integrating billing and automation walks through the connection and its failure modes.
When it is not you
If several unrelated clients report problems at the same moment, stop diagnosing accounts. One account with a problem is an account problem; four at once is a server or network problem, and working through them individually wastes the time you should be spending opening a ticket with your host.
Tell your clients something while you wait. A short message saying you are aware and looking into it prevents four more messages arriving, and it is the difference between a reseller who seems in control and one who seems absent.
When a client reports that one action fails while the rest of the site works, Managing ModSecurity Rules and False Positives covers finding the rule.
Several of these are website problems rather than hosting ones, and treating them the same way is what makes reselling unprofitable. What Support to Include and What to Charge For goes into the distinction.