Do bingo callers verify winners?
Yes — a claimed bingo win is checked before any prize is paid, by reading the numbers on the claimed card back and confirming that every one of them was actually drawn.
In licensed halls this is a legal requirement rather than a courtesy. Michigan's bingo rules (Mich. Admin. Code R. 432.21322) require a worker to announce the winning card's numbers back to the caller, who then confirms that those balls are in the master board. Colorado's rules (8 CCR 1505-2-3) require the caller, a floor worker, and a player other than the winner to verify the card together before the prize is awarded.
The procedure is the same wherever you play: read the card back number by number, match each one against the list of numbers already called, confirm the winning pattern is genuinely complete, and only then pay. Verify before starting the next game, because once the board is cleared the evidence is gone.
For a home or charity game, those three steps done out loud in front of the room are enough. Software can do the same check automatically against the called list.