Contempt - here's a offset 101 lesson.
Baseline is the 350Z, which has a +30 offset (actually the offsets vary between models and front / rear wheels, but we'll use this figure as a base).
When the advertised wheels have a bigger + offset, such as the +47 on the ebay wheels, and the wheels are the same width (ie 7.5" front), then the outside of the advertised wheels will be tucked in 17mm (difference between 47 and 30) towards the engine when placed on the front of the 350Z, compared to stock. This would look horrible, as I would want to have the outside edge of the wheels further in the opposite direction and closer to the wheel arch.
Now for the rear. Again there is a difference of 17mm in offsets between the 350Z wheel and the advertised wheel. However, the advertised wheel is 8.5" wide compared to the 350Z rear wheel which is 8" wide. So the 0.5" difference is about 12mm in metric terms. So the advertised wheel is 12mm wider or 6mm wider on the inner side of the wheel and 6mm wider on the outer side of the wheel. To determine where the outer edge of the advertised wheel will sit on the 350Z, it will be located 17mm inboard (due to offset differences), but will stick out 6mm (due to the wheel being wider). So simply subtract 6mm from 17mm and the advertised wheel will be tucked in 11mm on the rear of the 350Z compared to a stock wheel. Again, this is going in the wrong direction as you want the wheel to be closer to the rear guard and not further from it.
Look for wheels that have an offset closer to or a little less than stock.