Particular bad: A business will not be liable for errors in its tax returns if they were prepared by a certified provider. That means no penalties or fees for mistakes. -- What the bill actually provides is that a business that uses a certified provider will not be liable for errors "if the liability is the result of an error or omission made by a certified software provider." (Section 2.b.2.E of the bill) The business remains fully liable for any penalties, etc., that are due to errors or mistakes that originate with errors or omissions the business itself makes.
Other notably imprecisions: There is a "small seller exemption". If you collect less than $1,000,000 a year from out-of-state customers, you will have no new obligations under this bill. The small seller exemption applies based on remote sales the prior calendar year, so you'll never have any obligation the first calendar year in which you have remote sales, even if you have $10 million in sales out the gate, and you'll never retroactively become liable for taxes for sales earlier in the year as a simple $1 million/year threshold would suggest. OTOH, you also can will liable for remote sales taxes in a year where you have less than $1 million in remote sales, if it is preceded by a year in which you had more than $1 million in remote sales.
Online sellers will be required to collect, report and pay sales taxes in all of the states (once the states meet certain requirements), rather than only the states the seller has a physical presence in. Well, all of the states that (a) have sales and use taxes, and (b) choose to apply them to remote sales. Presumably, all the states that meet (a) will eventually do (b), but not all states have sales and use taxes to start with.
Each state that wants "remote sellers" to collect sales tax must establish a single entity to manage tax collection and audits for the entire state. Sellers won’t have to deal with all 5,900+ separate taxing municipalities in the country, just 50. This makes the typical mistake of assuming that there are 50 'states' in the sense used in the act, but that's not correct; 'state' in the bill are defined to include "each of the several States, the District of Columbia, the Commonwealth of Puerto Rico, Guam, American Samoa, the United States Virgin Islands, the Commonwealth of the Northern Mariana Islands, and any other territory or possession of the United States.", so there are not less than 57 potential taxing authorities.