UTENAGWomens Arch Support Flip Flops Comfortable Orthotic Thong Sandals

Are they true to size, or do they run big or small?

I'm a 9 1/2. If they're true to size then I'm assuming 10 is too big and 9 is too small?

Every time I buy adjustable shoes like this, they arrive pre-adjusted to the tightest possible position. Will I be able to make these tighter?