We did offer this awhile ago and had no problems but the only problem i forsee with this is, if someone has hyogonadism, steroid abuse etc and all of these factors we cannot disprove.
eg, we say money back guarantee if it doesn't work and it may not work if you are not a normal healthy functioning male and have had abuse of your HPTA. so in a normal case ie someone is 100% natural and has normal testosterone levels i would have no problem in offering someone like that a money back guarantee.
if someone else who has abused gear and doesn't have normal levels of natural testosterone it would put me in a situation to disprove their drug use in order to not pay out on a money back guarantee.
So yes if someone can absolutely without a doubt prove they have normal levels of testosterone to begin with i have no problem offering a money back guarantee.