In the Sales Setup you can set the posting date to be "Work date" as default, but when you make a sales order the work date is set on the order, and if you post that a week later it will be posted on the work date last week and not todays work date.

My suggestion is that, if you have set Work Date as the default date, you should get a warning if you post a sales order, that is not set to todays date - and the best if you can choose: [Today], [Posting date from order], [Cancel] to continue.