Who really pays transaction taxes like VAT or sales tax?
The issue you are asking about is tax incidence. This Wikipedia entry provides a good introduction. In short: it depends on how easily supply and demand respond to price changes relatively to each other, the so called price elasticity of demand and supply.

According to standard theory, it doesn't matter who pays (in the legal/fiscal sense) the taxes, as the burden of the taxes depend on economic circumstances. If demand falls rapidly with higher prices while supply does not, sellers/producers will lower their price (before tax), and therefore carry a relatively large part of a tax.

Of course, there may be all kinds of administrative costs and other 'frictions', that make it more or less efficient to have one group or another pay taxes. Also, there is evidence that people do change their behavior according to how the taxes are paid; see for example this paper, or this document.