I really love these shoes (I got the cork ones) but this is the 3rd pair of slingbacks I've had to return this year.  No one else mentioned it so maybe it's just me but the back strap doesn't have a buckle and is elasticized so when I ordered my normal shoe size, the strap was too loose and couldn't be tightened. I'm not sure if going down a half size or even a full size will help.  I think it will just force my foot further into the shoe and make my foot appear too wide (and be really uncomfortable).  I guess only straps with buckles for me but so loved the cork look.