I would think the impact on resale value will be slight over time. A year from now the market value of a used refurbished MK III will probably be very close to that of a used MK III, provided the number of actuations and condition are equal. However, the market for used, refurbished MK III’s may be thinner, i.e., some folks won’t be willing to buy a refurb. It sounds like you have a good deal in your hands, so congratulations. That said, I would use the one-week return period to verify that everything works as it should on the camera- things like light metering, focus-point sharpness, HDR, and whatever other features you plan to use.