But be careful because some companies actually switch shells on the even size while others switch on the odd. So company a might use the same shell for a 27 and 27.5 while company b uses the same shell for a 26.5 and a 27. So the difference between a 27 and 27.5 could be significant depending...
Shop guys need to eat too!!! I agree with this theory since the shop is taking all the risk. If something happens they are the ones who get sued not the e-bayer who sold it.