It can be given with a Destiny Knot just because the seller is being kind, there's no other reason lol.
If the Ditto is Shiny, it will have no effect on the offspring (unless it is of a different nationality, then you have to talk about the Masuda Method). Also, if the Ditto is 6IV, it's not guaranteed that all 6 will pass, but if the other parent is also 6IV then you are guaranteed 5IV eggs and have a 1/32 chance of getting a 6IV egg.