Around 2003, we started what turned out to be the largest data marketing company in the Netherlands. Telemarketing was booming, direct mail was big business, and people would answer surprisingly personal questions if you put them in an envelope and offered a reward.

We sent out roughly a million questionnaires a year, across the Netherlands. Fifteen to twenty per cent came back. People sat down and filled them in, sharing details about their lives and their finances that you would hardly expect anyone to put in the post today.

The original idea was to identify households that might benefit from refinancing their mortgage. A specific question, with a calculation behind it.

But the answers turned out to be useful for much more. What began as a mortgage proposition grew into a database marketing business supplying data to list brokers across the Dutch market, mainly for campaigns delivered by post.

Buying data from companies and organisations was more straightforward then, too. We checked its origins, kept the paperwork and dealt with a regulator that was already very much part of the landscape.

Whatever we bought, it was ours once it was in the file. We were ultimately responsible.

Our interest in handling complaints properly had a practical origin: we disliked receiving them twice. People received a quick answer, were flagged and were not approached again.

A consumer saying "leave me alone" had given us a particularly clear piece of data. It seemed sensible to use it.

The questions were on the kitchen table

Looking back, what stands out is how visible the exchange was.

You received a questionnaire. It asked about your circumstances. There was a reward. You filled it in and posted it back.

That does not mean everyone understood every subsequent use of their answers. But the act of handing over information was hard to miss. The questions were sitting on the kitchen table.

Today, the exchange is harder to follow. A banner appears, you click whatever makes it go away, and the thing you came for finally loads. We use a service because it is useful or entertaining. Understanding its relationship with our data requires a separate effort, usually at precisely the moment we would rather get on with whatever we came to do.

That tension is more interesting than the familiar argument that people either care about privacy or do not.

We can be happy to answer a personal question in one setting and deeply suspicious of it in another. Who is asking? Why do they want to know? What happens afterwards?

Those are reasonable questions. A company should have answers that survive being spoken aloud.

Having built a business around the commercial value of data, we understood the enthusiasm for everything it can tell you. We also knew that the person supplying it may have a rather different picture of the arrangement.

Technology has changed enormously since we sent those questionnaires. One simple test still holds: could you sit opposite that person and explain what you are doing with their information, without wishing you had brought your lawyer?

We used to pay people for their answers. The least a company can do now is give them a straight one.