Recently, I've been actively bidding on various and sundry covers with illegal uses of revenue stamps as postage. It's a bit of a minefield, as these covers are frequently contrived.
Additionally, the competition is quite fierce; I've ended up being the underbidder, or my bids not even executing because they're too short, quite a bit as of late. To those who lament the demise or malaise in philately, I say "phooey!" It all depends on the areas you collect. In fact, from the perspective of someone who's still in the acquisition phase of their philatelic life, I'd say it's a bit too active, dadgum it!
At any rate, I won the cover below at considerably less than I was willing to pay, which always makes me suspicious. However, upon receipt and examination, I can find no evidence of contrivance. The "Coals Mouth" cancel ties the leftmost stamp, and there are additional strikes of the same cancel on the two other stamps, and there is a correct 2x penalty marking "Due 6" at left.
When people manufacture covers like this, they usually use low-to-medium value stamps (R2c catalogs $210 for a single and $450 for a pair), as it's typically not worthwhile to create something with components whose intrinsic value is almost as much as that of the item being created.
The bonus came when examining the stamps, revealing the single and left stamp of the pair to have previously unrecorded plate scratches. It first appeared that if you were to place the single above the left stamp of the pair, they might comprise a single continuous scratch crossing both stamps... which is a possibility as the stamps conceivably would have originated from the same sheet. However, the angles of the scratches look like they are different.
So that just means more plate scratches to document and plate.