I assume that referencing a Milestone is not sufficient for a vendor (exchange). That is, they must be making sure that both a Milestone is referenced AND that some time or cumulative weight threshold is acheived.
Given that, what is the absolute minimum cumulative weight that a transaction must have to be considered confirmed by a vendor?
What are the IOTA Foundation's official recommendations?
There are no recommendations out yet, because we still need the coo to prevent double spends.
In the whitepaper it stats that the confirmation status of a transaction is given by the percentage of tips that directly or indirectly reference this transaction (http://iotatoken.com/IOTA_Whitepaper.pdf Page 3). If we select 100 random tips and 70% of them indirectly reference our transaction, it is 70% confirmed.
However, it is unclear how the coo will be removed/decentralized. Depending on how confirmations are defined in the future we will get some recommendations for sure.
