Skecherswomens On-the-go 600-15304 Flip-Flop

I usually wear an 8 in boots, running shoes, etc. but I wear a 7 in flip flops. Should I stick with a size 7 in these?

If i normally wear 8.5 what size should i get?

If you wear 1/2 size should you size up or down? So I wear an 8.5 should I go 8 or 9?

I've missed the return window by 6 days. I've never worn the shoes. I'd it possible to get an extension?