What do you think?
I think you are being silly and ridiculous.
Here's a transaction from the blockchain:
https://blockchain.info/tx/a244cbca647ad9cdd01fe7d79744916857dd26360e2d284b81599e5e689e8904Since you think that "ever bitcoin transaction of a company/brand is open and public in every computer mining it! Everybody know to whom this company sells/buys, which sums, etc etc" . . .
Looking at that transaction in the blockchain, please tell me who owns the address 1ajECz2AtEZpXfvit9977Rgid11Y7AexS ?
If you can't, then please consider that your statements are a waste of time.
OP was over-egging it, however there is a point to be made I think.
If a company was not careful in how they handled their addresses, it could be possible for someone who transacts with said company to find their other addresses.
Much like it is possible to find an exchange's hot wallet or cold storage.