Texas State Utility Tax Exemption

Has anyone heard of this?  We were recently approached by someone claiming to be able to get sales tax exemptions on electricity tax.  If its for a residential use.  They work on a contingency fee and can back date the bills for 4 years. Has anyone else seen/done this and have a recommendation on the vendor they worked with  ?  A little research makes it look like it is a legitimate expiation. http://www.window.state.tx.us/taxinfo/taxpubs/tx96_1309.pdfYou can also research Rule 3.295 of the State Comptrollers officeHere is an example of a company doing this type of work (not the specific vendor I am referring to )  :https://www.utilityconsultantsinc.com/faq.htmlLooking forward to the responses on this. Thanks