MVVM: Decouple Model from ViewModel

Everyone will have their own opinions on this. Personally I don't mind using the model directly in the view model. For me, the whole idea of a view model is to extend your model in such a way that it can be consumed by a view.

A simple example of this would be person object, It would have model properties like like name and age for instance. When I get to the view model stage I may add properties to it like visibility which would not make sense on the model proper.

Another point to note is I would consider a model to be the data and the view model to be the context. So you may have a "Card" View Model for a person but you may also have a "List Item" view model that represents the same model in a different context, with different view model specific properties.

I do tend to make my models up using interfaces where relevant and use Inversion of control to inject them into the view model, that way the only thing my view model actually knows is that it needs an IPerson and that it will be provided in the constructor.

As I said other people will have different ideas, all are correct and its up to you to work out which one suits your needs.