Question

How could the legal expenses incurred in establishing rights to assess remote sales and the costs that states incur in collecting such taxes cut further into dynamic analysis estimates of the net revenue gains to states from implementing the taxes ?

Short answer

Legal rights to assess remote sales and costs to collect these taxes - depict that the tax base from these sales reduce, as per dynamic tax analysis.

Step-by-step solution

Basics 

Static Tax Analysis : mentions that tax revenue increases infinitely due to rise in tax rate, as the tax base (taxable amount) remains unchanged.

Dynamic Tax Analysis : states that tax revenue increases till a certain optimum point due to tax rate increase and decreases afterwards, due to initial raise and gradual fall in tax base.

Explanation 

So, as per dynamic tax analysis - rise in tax on remote sales decreases the tax base from it by a huge extent.

There have been empirical evidences stating that a low tax imposition of $4\%$on remote sales reduces them and the corresponding tax base by $15\%$.

So, the state's estimates of remote sales' tax are over estimated, and the actual lesser tax from these is outweighed by the cost incurred on collecting them.