Is this inspired by S.T.A.C.K.E.R. or did you come up with it on your own?
lg.newImage("cat.png") -- made possible by lg = love.graphics
-- Don't force fullscreen (it frustrates those who want to try your game real quick) -- Develop for 1280x720 (so people can make HD videos)
I would suggest only having the salesman say "Thank You" when you get a complete Tetris (that would be when you clear 4 lines). Otherwise it would just get annoying. Also, maybe you could surround the blocks with a faint outline (perhaps only after they've been placed down) so as to ease the visual hampering caused by the irregular shapes.