Have a look at http://www.askdavetaylor.com/how_do_i_set_up_a_computer_repair_business.html
, which discusses this problem.
You have to bear in mind the possibility of physically damaging the computer as well - say you dropped it, for example. I don't believe that would be covered by such a waiver. On the other hand if you feel that is a remote possibility (e.g. you don't foresee actually physically handling the goods) then you can probably ignore that possibility.
I am not a lawyer - if you have access to a tame (or cheap one) it might be an idea to clarify what your liability would be. I guess it varies from country to country. Better that than finding out the hard way!