When doing an appraisal, you have to borrow the original from the owner to examine the painting's authenticity and condition.
Literal
Appraisal [object-を] do time [at-には], painting [possessive-の] authenticity-or-forgery [and-や] preservation-condition [etc.-等] [object-を] examine [purpose-ため], owner [from-に] real-thing [object-を] borrow-[listing-たり] must-do-becomes.
真贋 ('authenticity and forgery') is a Sino-Japanese compound pairing 真 'genuine' with 贋 'counterfeit' — a compact way to say 'whether it's real or fake.' The sentence chains several formal constructions: ~時には (when), ~為 (in order to), ~たりしなければいけなくなる (come to have to do things like). The last verb cluster is heavy but natural in written explanatory prose.