Well, it is possible, theoretically. But practically, you would have to get really close to the reader, several millimetres in fact. That by itself is quite improbable, plus the readers are deliberately placed “above the pocket level” of an average passenger to avoid such situations.

The system calculates your optimal fare during the night of each day (between 3 and 4 am) and only then it charges your bank account with the final amount.
The Mastercard cards always make a czк 1 collateral immediatelly after beeping, which is later erased and replaced with the actual fare. The transaction always takes at least three days, so do not panic if you see nothing in your e-banking.
The Visa cards, on the other hand, do not require the czк 1 collateral and charge your bank account daily with only the final fare amount.

No.
Just as a validated paper ticket, it is considered to be “used”.

No.
If you purchase a wrong ticket from the terminal (like a full fare ticket instead of a reduced one), the transaction is, unfortunately, irreversible.
That is why you must always check the purchase overview thoroughly before you finish the payment.

Of course.
The long-term pass on your card counts as a ticket for you personally, but you can still use the same card to buy tickets for your friends or additional tickets for suburb fare zones for yourself. Or you can check the validity of your long-term pass from time to time. And if you want, you can beep with your card just for fun — if you have a pass on that card, no money will be deducted from your account.

Of course, suit yourself.
But be cautious! If you use one card for checking in on a short-term ride, make sure you use the same card for checking out. If you don’t, the system will charge you two separate basic tickets, because we have no way of knowing those cards belong to the same person.

Of course.
Just don’t forget to show both of those tickets to the eventual ticket inspector.

That, unfortunately, is not possible.
If you are travelling outside Brno, you must plan your journey in advance and select the ticket from the menu accordingly. If you forgot and just checked in, then it would be necessary to purchase the ticket for an additional zone during the ride. When travelling in the opposite direction, this mistake cannot happen, because the check-in system is not active in the suburb zones, which forces you to purchase the ticket from the menu straight away.

No.
The sysem can count only up-to a 24h ticket and charges you every day during the night, so after multiple days of beeping, it would charge you multiple one-day tickets instead of one multiple-day ticket, which is quite a price difference. If you want to buy a multiple-days ticket, go to the Brno city service portal at BRNOid.

Of course.
Paper tickets are still being sold in shops, in ticket machines and by drivers. All the terminals are still equipped to validate paper tickets.

Yes, that is theoretically possible.
But it’s starting to sound like you are deliberately trying to overcomplicate things. If there are three of you, you can, for example, select tickets for 15, 60 and 90 minutes from the menu. As soon as you purchase them, they are all valid and the three of you must then leave the vehicle one by one before the validity of each ticket ends. And the last man standing must be the one holding the card. That is the crucial part of this little heist of yours.

Of course.
Just go to the BRNOidwebsite and you can download as many invoices as you want to. There are three ways to do that:

1) If you have the electronic long-term pass or you just have an account at BRNOid, just log in and browse the list of all your tickets in the section “My tickets”.

2) If you don’t have an account at BRNOid, just insert your card info and the site will generate a list of all your tickets.

3) If you are paying for the tickets with a phone (and therefore you don’t have a card number) or you just don’t want to give out your card info, go to BRNOid and insert the number of the transaction from your e-banking system to view the invoice for the individual ticket.

If you bought the ticket using your phone and you need the invoice immediately (before your bank processes it) you can use a special app for reading virtualised cards, which is available at BRNOid including instructions.

Nothing.
If the system recognizes a card with a long-term ticket or pass associated with it, no additional fee is charged to that card when you check in. Only if you select a specific ticket from the menu (like a ticket for a friend, for a dog, etc.) the system will charge you.