Is it doable to wear sandals a size under my actual size?

I just found some sandals in a second hand store that I really want, buuut the only ones I was able to find are a size less than my regular size. I wear a size 40 which often fits loosely, 39 for a tighter fit, these shoes are platform strappy wedges in 38. Obvs it would be hard to return them should they not fit and they’re not that cheap so I’m wondering if I should go for it or wait for my normal size to be available if it ever is. Thanks!