I looked into this a bit. I believe many of the states that cared about this issue worked together on the new internet sales tax law. there is a provision to excludes smaller sellers, basically if you make sales less than $100K or less than 200 transactions per year to the particular state, as a retailer outside that state, you don't have to collect state sales tax and submit the taxes to the state. however, the rule changes for marketplace platforms like eBay or Amazon, basically the rule treats the marketplace as the seller and the rule applies to all transactions via that marketplace, even if the actually seller is just selling one-off personal stuff from their attic for $5 and not operating as a business.
it's both a pro and a con for sellers/buyers. as a small seller, you might see decreased sales or need to reduce price due to the +10% in sales tax. as a larger seller, who would normally be required to keep track of all the sales tax for different states, if you sell through a marketplace exclusively, the marketplace simplifies the tax collection and does it on your behalf.
The problem is that a lot of the state/county/city laws still contradict the federal laws. Many cities require taxes remitted to anything sold to residents of the city, or the residents must file use tax for the items (most don't). Now, the problem is that every city has different rates, so the counties, and so are the states so it's a HUGE undertaking to know where and when you should be collecting and remitting taxes. I've done this before and it didn't matter if I sold just one part to one customer in a particular jurisdiction--they wanted their cut.
It's interesting the marketplaces are being treated as the national businesses they are with 'inventory partners' providing inventory on their platform. Since they collect the payment, take a cut, and pass on a bulk of the revenue to the 'seller' (who basically is just getting paid for their inventory contribution and a portion of the profit), it makes sense that they are treated as the seller. Now, what sucks about that deal is that while they are the seller, they are not responsible for any of the products sold and yet are in charge of the customer service which is basically 'customer is always right'.
Since all the taxes are coming to everyone at the same time, it really shouldn't affect prices as everyone's jumped the same percentage--the tax percentage. And since the percentage is based on the buyer vs the seller (should be anyways), the same company selling the same product from two different places at the same price should be on a level playing field.
There are companies that provide tax remitting services for those that have to do it in-house. You can also go without assistance as I did in a previous business, but it is a daunting task keeping up with all the different rates and making sure you're collecting the right amount. And then there's the monthly filings for all the remittance. It took me a good couple of hours every month and that was even with a spreadsheet and reports out of our point of sale system. Luckily, most of my customers were wholesale, so there wasn't that much to collect/remit, but you had to file each month forever, even if it was a zero filing, so that was upwards of 40 returns a month.
This whole system can be simplified to a great extent using the same systems that credit card companies use for their merchant and interchange fees. It's all done automatically and daily so there are no monthly filing issues. The same could be done for taxation--the federal government provides the tax information in an electronic format to every retailer required to collect tax. This format is standardized so that point-of-sale makers can quickly and easily update their systems with any new tax information. Location information is capture at the sale and the appropriate taxes are charged and collected. Each day at the close of business the totals are remitted to the federal government and reports are sent to the retailer to reconcile with their point of sale records. The Federal government distributes the payments electronically daily to each state, county, city that is supposed to get their money. And the federal government is in charge of reconciling with those that remit to, while the retailer simply has to reconcile with the federal government.
This entire process would be just like reconciling credit card batches like businesses do regularly so the burden on all businesses would be minimal, the federal government would be doing their job, and the states, counties, cities would be getting the money they're supposed to. Win-win-win.