if you can get them to do a test fit with the rim or even better with rubber on to see if it is the right offset for the car and dosn't rub on anything.
eddii the rim in that pic would be a wider rim than a 7.5 or 8. in order to get that much dish you would need a wide rim, say at least a 9 inch with a tough (read low) offset. That rim looks like the 19 x 9.5 with an offset of +25-28. We all know something like that wont fit with some serious guard and fender work.
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For somthing like the rims you are after I think (not 100%) you would be looking around the +38 - +40 area. But don't quote me on it it's just a ruff gess.
dish - the amount of dish depends on offset. the lower your offset the bigger dish you will have. a wider rim (eg. 8/9inch wide) will also have an effect on dish.
offset -18x8 rims with the usual +35/34/37 bob jane tmart offset can allow 3-5cm of dish from when i did some calling around a while ago, depending on spoke design.
offset should be stamped on the back of the rim. if not its on a sticker with the size and width of the rim.
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you may have to remove the plastic guards behind the wheel arches if your car is preety low