You can request the appraisal district's evidence under section 41.461 of the Texas Property Tax Code. We recommend you make this request by certified mail or in person (make sure the appraisal district date stamps it). You must make this request at least 14 days prior to your hearing.
Sec. 41.461. NOTICE OF CERTAIN MATTERS BEFORE HEARING.
(a) At least 14 days before a hearing on a protest, the chief appraiser shall:
(1) deliver a copy of the pamphlet prepared by the comptroller under Section 5.06(a) to the property owner initiating the protest if the owner is representing himself, or to an agent representing the owner if requested by the agent;
(2) inform the property owner that the owner or the agent of the owner may inspect and may obtain a copy of the data, schedules, formulas, and all other information the chief appraiser plans to introduce at the hearing to establish any matter at issue; and
(3) deliver a copy of the hearing procedures established by the appraisal review board under Section 41.66 to the property owner.
(b) The charge for copies provided to an owner or agent under this section may not exceed the charge for copies of public information as provided under Subchapter F, Chapter 552, Government Code, except:
(1) the total charge for copies provided in connection with a protest of the appraisal of residential property may not exceed $15 for each residence; and
(2) the total charge for copies provided in connection with a protest of the appraisal of a single unit of property subject to appraisal, other than residential property, may not exceed $25.
http://www.dallascad.org/forms/protest_process.pdf, scroll down to page 10