Retubing Question

I just got my amp back from ARC corp with new 6922 signal tubes installed. I have seen on audiogon,the same tubes for less then half the price. I know ARC has some markup in the tubes it sells. Now my question. Could I have done this myself, buying the tubes off of audiogon and saved some money,Or do the tubes need to be adjusted in someway. I understand about matched sets, and I do not have any equiment to test the tubes. As you can tell,I am just learning about tube replacement. Thanks for your feedback.
Brouch