In your first example, the miscellaneous parts were back with the tractor BEFORE they were sold. I see that at auctions and agree in some cases. What about all the people that may have shown up that may be looking for shields or covers? Tractor buyer won, parts buyers lost.
In your second example, you indeed made a profit, so I am not sure how that is any different. Unless you feel that your profit was reasonable gain, but not price gouging. But really, you paid $10, how are they suddenly worth $150-200. They are worth $10, thats what you just paid for them.
For the original loader example. I doubt the interested bidders on the loader knew the brackets would appear at the end of the auction, otherwise they would have bid higher. I imagine they bid knowing they would be searching for brackets. The buyer got lucky, plain and simple. What if the buyer of the contents of the building just happened to buy the contents to get the loader brackets? At that point it is back to the auctioneer not doing a good job of prepping.
Dont take my comments as negative, but I am of the position you should know what you are bidding on, and bid accordingly. Once the hammer has dropped that is the contract you entered into.
All the other talk about making tractors not start, switching items around on pallets on purpose, that is a whole different subject.