I'm now working with Prestashop for a long time but I must say some parts of the system system have serious flaws for any business that wants to automate all. In most EU countries we are bound to strict ecommerce rules.
Below my remarks:
Invoices
The biggest problem with the invoicing system is that created invoices are not "frozen" in their state when they are generated. That means that when changes occur or are made all invoices are changed to these new settings. Imagine this scenario: at a certain date we decide to change a few settings for invoicing. These changes should only apply to newly generated invoices because old invoices are already received by customers. This is a problem, when changing settings a customer that logs in again also gets the new invoice layout, that is very very wrong according to the strict rules we have in the EU. If a company gets an audit by the VAT organisation this is a real tricky situation.
After an upgrade you cannot actually freeze old invoices, this has disaster written all over the place. An option to disable invoice access on a per customer base would solve it.
In version 1.5.4.1 there are also rounding errors on invoices which is a big problem. Especially orders without shipment get rounding errors in the range of 5 eurocent. Have checked v 1.5.6. but seems to be the same problem. Again, cannot test the upgrade for real because it changes all existing invoices again.
Another problem is if you switch off invoice access for customers, currently it disables automatic invoice sending but also invoice access. These need to be two options: enable invoice emailing, enable customer portal access to invoices.
Multiple customer types
PS does not handle this 100% perfectly. On account creation we cannot assign customer groups or tax groups. I want to have groups based on: EU customer with VAT number, local customer, EU customer without VAT number etc. This is not arranged in a proper way and so it can happen that a EU customer sees some VAT mentions on his invoice which is wrong. I have tried and tested every single option but for an EU customer with VAT number there is still VAT mentioned in the head of the invoice (product incl. VAT and product excl. VAT) lines.
B2B
It is very unclear how B2B can solve above problems, have tested it but not sure what it exactly does besides new fields and price management. Some of the new fields are actually only needed in France :-) Much more info would be welcome.