I have noticed that there does not seem to be anything which logs which users approved the quote. Furthermore looking at the database tables it would seem that the quote status does not keep a trace of its history something that could be needed in many cases.
Currently, i see no way in the system to prove to a client that they logged in and approved a quote.
What i suggest is to add a table which keeps a history of the status of the quote (or invoice) and a report that can show which user changed status of which quote and when.
In this way one accountant from a client cannot deny that his/her colleague approved the quote or any similar situation.