Taxi may be a lot of things, but a scam is not one of them. They are a company that does exactly what they say they are going to do, at exactly the price they say they are going to do it for. There is no upsell, and they take no vested interest in the success of their members. If you land a deal that makes you $50,000, Taxi's cut of that is $0.00
Also they host the Taxi Road Rally every year which is a really cool conference. It is free for members plus a guest. Basically $150/person for one of the better music conferences I have been to. Even if you never do anything with Taxi but the conference its still a good deal.
In full disclosure, I do not work for Taxi (never have), but I have spoken at the conference a few times and know people that work there as screeners (the people that listen to and evaluate the music). One of the biggest problems with a lot of member that have no success seems to be people that do not pay attention to what the record company. publisher, music supervisor, etc is actually looking for. A label could post that they are looking for a young artist in the style of Justin Timberlake, and all these blues bands with guys in their 40-50s send in their music for the listing, then bitch to people that Taxi sucks because nothing ever happens with their music...