Mahjong means you declare the hand complete. In American play that is 14 tiles matching one printed line.
Chinese play is usually four sets and a pair, plus the table's scoring. Riichi is a 13-tile hand that needs a yaku. Taiwanese wins on 17. MCR needs eight fan.
Ask before you sit: is the win sets, or a line on a card?
Ask what a win is
American play is 14 tiles matching one printed line. Chinese play is usually four sets and a pair plus the table's scoring. Riichi is a 13-tile hand that needs a yaku. Taiwanese often deals 16 and wins on 17. MCR needs eight fan.
If the tile count does not match, stop and ask.