Floyd Mayweather -- 'Crossing My Fingers' ... For People to Buy Fight Tix

Floyd Mayweather doesn't really have a solution for his big ticket catastrophe -- saying he's merely crossing his fingers and hoping that sales go up for his retirement fight with Andre Berto.

Floyd faced the media Tuesday -- where he was asked straight up if he was worried about the shocking lack of interest in the Sept. 12th bout ... with thousands of tickets still unsold.

"I just try to stay positive and keep my fingers crossed and hope for the best," Mayweather said.

Floyd then kicked the question over to Mayweather Promotions CEO, Leonard Ellerbe -- who said the slow sales are NOT concerning at all ... "normal business."

Yeah, maybe for most people ...