I think the workers there hear a lot of things from customers. It can't be an easy job. I have sympathy for them. But yes, they could at least check to see if a mistake has been made. Better that way than having customers upset later on over not buying what was advertised as for sale.
All mallard derived ducks have males and females with the same juvenile plumage. I think this one is too young to do the voice test with. I believe it is 12+ weeks for that to be accurate.
They're too dark to be lavenders, imo, so I think you are right that they're blue. Whether they are Orpingtons is another matter.
The one in the background of the second picture has a touch of reddish color on his head, so that one is probably not an Orpington.
The others could be, or they...
Second to the last one is male with that elevated, bulbous comb. I think the last one is, too.
Satin Silkies have purple, irregular combs just like regular ones, but by 12 or 13 weeks, male specific feathering should be apparent in males. They may start showing gold leakage on the shoulders...
They look a little young to be sure, but I do think you have a lot of boys.
1 Looks to be male, but rose combs can be tricky
2 Comb has some color, but it is not as bulbous as the first one, so could be a female. Time will tell.
3 female
4 male
5 male
6 female
7 female
Marans, 1 female...
If you had a light Brahma hen then I could see that and the olive egger rooster being the parents. But I would think a chick from a black Brahma would be darker.
I mention this because she does look a lot like a Brahma. Her legs are heavily feathered and her plumage is a bit loose and fluffy...