Where does my customers’ information sit?
In your accounts. Not in a shared one of mine.
That’s the short answer, and it’s the one that matters. What follows is the longer version, because if you’re the person who’d be answering for it, a short answer isn’t much use.
There is no big shared database with everybody in it.
A lot of people who build systems for small businesses run all their clients inside one setup they own, with a column saying which row belongs to whom. It’s cheaper to run and it means every one of their clients’ customers is one query away from every other.
Your customers’ details sit in accounts opened in your name, that you hold the keys to. It doesn’t pass through a company of mine on the way in or on the way out, and if you and I stopped working together tomorrow it wouldn’t move anywhere, because it was never anywhere else.
The part worth understanding properly
Nobody can reach across from another client. Including me.
Every client gets a separate key that opens only their own files. A request for anyone else’s is refused before our code is even asked.
That last part is the whole point, and it’s worth slowing down on. Almost every system that promises to keep clients separate does the checking in its own software — it asks itself whether you’re allowed, and answers itself. That works exactly as long as nobody makes a mistake in that software, which is a promise about carefulness rather than a guarantee.
Here the refusal happens underneath, in the layer that hands out the keys. By the time a request would reach anything I’ve written, it has already been turned down.
So it isn’t that I wouldn’t look at another client’s files. It’s that I couldn’t, and neither could anybody who got hold of my side of it.
What that means for the things you have to answer for.
If someone asks you to delete them
It happens, properly, and you can show that it did. You aren’t dependent on me finding time to do it, and you aren’t left explaining that a copy might exist somewhere in a supplier’s system.
If someone asks for a copy of what you hold
You can produce it, because it’s in one place and that place is yours. Most of the pain in these requests comes from the information being scattered across four systems that nobody has full access to.
If you ever have to describe the arrangement to someone
It’s a short description: it’s in our own accounts, a supplier has access the way a member of staff would, and that access can be withdrawn by us without anything stopping. That’s a much easier conversation than the alternative.