There is no implication that van Richten would be an Unreliable Narrator, and the fluff text obviously won't lie.

Van Richten's journal, on the other hand, claims he killed them all.

Ezmerelda d'Avenir's fluff claims that she was part of the clan that kidnapped Van Richten's son, but that van Richten spared them after interrogating them, since he had gotten the information he needed.

The module never actually clarifies what the Dark Powers are beyond the name as written it could just be an alternative name for the vestiges. The book also mentions Strahd making a deal with the Dark Powers for his powers, but also says he became a Vampire thanks to one of the vestiges from the Amber Temple. In this version, he made a deal with one of the vestiges in the Amber Temple, but the text in his Tome referencing Death is unchanged.

In the original Ravenloft lore, Strahd became a vampire through making a deal with an entity called Death.

Many of them are willing to bargain because they expect the players to die, allowing them to get money, and their goods back. Thus they either charge at such ridiculous prices, or just don't bother to really price fairly because they have no reason to. Most of the shopkeepers are apathetic or fully aware of the hell they are stuck in it.

Adam Smith Hates Your Guts: Justified.The book explicty states that Ireena is one thing that can make him go off rails, and a careful group can use this to their advantage. Achilles' Heel: Besides your standard weakness' a vampire would have, Strahd has another one in the form of Ireena.

Curse of strahd dark gifts