Thanks to all of the above. Now I have a clear mind.
n_K, on 04 January 2013 - 14:15, said:
NEVER use the root account AT ALL once you've configured the MySQL server, make another account and grant it root-like permissions and ONLY use the root account as a last resort if something breaks to restore everything.
Yes use different accounts for different sites, one account for all clients on one site should be fine i.e. one account for this receipt tracking site, another account for a control panel site, etc.
I shall take this recommendation then
technikal, on 04 January 2013 - 14:28, said:
I don't really see the point of having totally distinct tables for each user either. Seems like a lot of duplication and you'll end up with a massive amount of tables.

There was no other way my logic could function.
I Googled a bit and found that there wasn't any problem having multiple tables. The thing is that it allows flexibility. I didn't see a good way on putting the client info, the receipt #, the quantity, price of the product purchased (because it has a variable price), the current product id, the tax, and whether it was paid, delivered or not. So I could fetch it in a productive way later on....
Anyways, I'm open to suggestions