Lying about profit being made

assalamu alay kum warahmatullahi wabarakatu mufti saheb
. hope you well
. i recently heard a lecture whereby a mufti said that do not tell your customer that you are making R5 on an item when you are making R10 on that item-that prompted me to ask you this question as my director uses this phrase alot.
if person a is selling a shirt for R25 and in selling it to a customer he says that i promise you i am only making R2 on a garment or kasam i am only making R2 on a garment meanwhile he physically paid R20 for the garment to the supplier.
is this jaiz?
If yes then what factors should be taken into account when determing the cost?(would it only be the cmt paid and fabric price or will overhead expenses be included as well?)
make maaf for any taqleef caused
. jazakallah