As mentioned in my above response, there are many ways to show professional demeanor, attitude and culture that is practical and verifiable. For higher up positions, it will be always a referral call, but that is a lot of work to do for intern/entry level/medium level engineering to the which you usually lack an unbiased referral source.

Also, its delusional to believe a resume is not a selling tool. There are good and bad resumes and its pure salesmanship. Finally, you will have to prove that there is a correlation of any kind between salesmanship and technical ability.

A hire is a full package deal. If you interview a total wiz, but he comes to the interview naked, you will not hire him. Well, I doubt I would vote for a hire.