It is quite clear to me, that there are a lot of people out there, who wish to purchase their discus fish as small as 2.5”.
There is nothing wrong with that !
However, this is only the case if for one you are experienced in Discus fish keeping, and two, you fully understand that at this size they require a regular feeding regime.
In order that they might reach there full growth and potential, the regular regime of water changing and feeding must be followed.