Account Executives (and pretty sure everyone in the sales division all the way up to the VP of Sales) had no direct way of removing reviews (and I strongly believe this has not changed). When I was there, the only way for an Account Executive to have a review removed was to email customer service and provide a solid explanation as to why it violated the review guidelines. And I can tell you that many times it wasn't easy; customer service had strict guidelines to follow and I (and my friends) had plenty of arguments that went nowhere. Theoretically, an Account executive could make friends with a customer service rep or someone on the development team and try to persuade them to remove a review, but this is highly unlikely because if found out, everyone involved would be fired (so there's a huge risk) and I can tell you from personal experience, removing a few reviews is not going to make or break a sale (so it's not worth the risk).
While it was a (sometimes extremely) frustrating process, I feel it speaks to how the executives of Yelp really do believe in the integrity of their review guidelines.
As for reviews being deleted, I can tell you that in many of those instances, the review has been put in a "purgatory" where the system waits until it receives a signal that the review is not actually spam to let it surface back up to users. This happens to both positive and negative reviews; there is no scam going on here to hide negative reviews for businesses that pay and positive reviews for businesses that don't.
Why isn't Yelp more transparent about this process and their algorithm? For the same reason Google isn't transparent about their algorithm - to prevent gaming the system.
With the frequently repeated story of business owners being told that their negative reviews will be removed, I believe it comes down to a misunderstanding of the sales pitch (the majority of the time). One of the key points of the sales pitch involved moving a positive review to the top of the review order where a positive review would stay for the duration of the contract. This was especially effective for completing a sale if there was a negative review on top ("the first review your customers see will always be a positive one"). So if a business became a Yelp advertiser, the review order would change, but only with that one review that was moved to the very top. No reviews were deleted or otherwise manipulated.
Why do I believe it's a misunderstanding on the business owner's part far more often than a mistaken or even purposeful effort by the Account Executive? For one, Yelp is pretty damn serious about their rep and will fire anyone caught doing this on purpose right away. Also, Yelp's training was good when I was there and has become phenomenal since I left so I don't see many mistakes happening. Finally, and I'm not going to butter this up, there are a LOT of business owners out there who don't understand the web and plenty who are just plain dumb (Just because you own a business, doesn't mean you should). the majority of businesses we called are one off restaurants/bars (just look at the majority of restaurant websites), little retail stores or one man service shops.
Yelp is about the customer first and businesses second; because of this, there are always going to be business owners who feel screwed. With all that said, though, I feel that this latest lawsuit speaks to a huge problem that is only going to get bigger for Yelp as it gets closer to an IPO unless they significantly change their business pitch.