Especially when it is dealing with new age woo-woo. We have clinical trials to avoid all the bias and filtering problems that scientists and test subjects bring into the study.
New-age beliefs, auras ect. are the most subjective kind of evidence and thus highly susceptible to one's 'filter-bias,' emotions, believes, desires, etc. In other words you see someone else's aura through the lense of your own.
While technologies are growing to see bio-photons and photo-luminescence, these have nothing in common with the aura readings that quacks sell at new age shops.