Honestly, if the safety activates at all positions, it is probably a good sign that it has CGW parts in it and that is a good thing. If it doesn't have CGW parts, then a new sear/safety may be in order but that isn't that difficult to fit. I'd ask the seller to check the safety function and describe if it is possible at all hammer positions. Also have them confirm the safety when actuated properly with the hammer at full cock, does in-fact prevent the hammer from falling when squeezing the trigger.
If you are really worried about this, have the seller take some detail photo's of the action, barrel, and hammer areas and post them up here. We can help identify if there is anything abnormal/gunsmithed already. Ideally field stripped pictures at minimum.
The part that would cause this is the sear leg to safety lug fit. The CGW adjustable sear has a setscrew that is used to ensure the safety is 100% reliable without removing metal. The set screw is smaller than the stock sear leg and thus allows the safety to be engaged at other positions than originally intended. This is not an issue as you shouldn't be applying the safety with the hammer down, it is a fully safe condition to carry/operate the firearm with the hammer down and no safety.
Cheers,
Toby