Buying comfortable shoes is all about the fit. The foot of your sandal should be smaller than the sole and care needs to be taken that the sandal should not hang over the sides or the back. Also you need to make sure that the toe box is large enough and it can accommodate the widest part of the foot. It should be important that the strap should be comfortable and should snug without it rubbing on foot, toes or back of the heel. Ensure that the sandals are not very big because the feet can slide around which can cause blisters on the toes.
I love my walking sandals because it is made of high quality materials. Suede, leather and fabric straps lets the feet breathe and prevents blistering. Look for straps made of polyurethane or nylon webbing that is amazing for water activities. Also take care that the foot bed should have a breathable fabric and can reduce sweating and slipping. Look for top soles that are made of memory foam or durable rubbers as they last longer and offer better support and protection.
The sandals should have a proper placed strap which can cause irritation, corns or blisters. Sandals that have back straps can hit below the ankle and it provides a secure fit and is comfortable. Make sure that you avoid the straps that rub against the foot top. The straps that are lined with soft leather or suede can prevent chafing. The element designs or seams can rub and dig into the feet to cause discomfort.
The sandal should also provide a lot of arch support. This will prevent cramps, fatigue and back pain. Look for sandals that allow all day walking as most of the sandals do not offer the arch support for extended wear. The sandal that are spongy, have supporting midsoles and support the arch lets the wearer be comfortable and wear it for a longer period of time.