Price sales e purchase

The client that connects via web access also to its Assetts and can also view the sales price and the purchase price?

Yes, Customer Web user can see the price they paid for and other data from the Asset Details tab (in RangerMSP Windows app term). However, they cannot see data from Vendor tab (including Vendor Price).
The easiest would simply be to create a "dummy" Customer Web user and log in yourself and see what they can see and what they can (and naturally, all depending on the Web User privileges you assign to them).