Having being a client of Vectis for nearly 20 years and also other auction houses included, all your theories are pretty true to a degree but the plain matter is all auction houses want to sell, its about the commision only to them as that is what pays all their overheads and makes them profit.
Using Vectis as a good example, they get plenty of product week after week and really dont need to set reserves, a few items in a 500 lot sale might have a sensible reserve but not a heavy one as they have learned by experience that high reserves dont make an item sell, its better for them to start at 50% of bottom estimate and let the lot find its value on the day, hence the reason you dont see the same items listed sale after sale unless a buyer hasnt paid or they have returned them as it wasnt as descibed, or it got damaged in the post.
As for the shill bidding, running items up carry on, well who knows......the commision bids left on the book is up to them to decide what price to start the item at. If a buyer leaves a bid for £500 on an item that is estimated at £50-£100, its up to them where they want to start and everyone can make theories and speculate how it all works, but in Vectis there are only two people who make this decision and that will always be unknown to all of us.
Regarding other auction houses, the same rules apply really, and in all of them, its business and Im very certain they will all have their little perk now and again, but this is life..