Over time, with so many nautical enthusiasts wearing these types of shoes around, the boat shoe became a status symbol as much as a functional piece of sailing gear. The style became popular with people from all walks of life, even if they had never stepped foot on the deck of a boat. As a result, the boat shoe is now a style of shoe as much as anything, and wide gap exists in the quality of a boat shoe designed for sailing and one that is simply styled on the technically superior shoe.
A good pair of boat shoes should fit snug, but comfortably. Your foot should not slide side to side or forward and back, yet your toes should not be cramped in the toe box. The most important feature of a boat or deck shoe is the sole. Boat shoe soles should have a lot of grip and really keep your feet where you plant them. The whole purpose of deck shoes is to help keep you upright on a slippery deck. Sometimes with laces, but more often without, boat shoes are also designed to be easy to sip on and off.
Most quality boat shoes will be made of leather, and you can treat them with various kinds of leather conditioners and waterproofers. Products specifically made for extremely wet conditions are available for the best protection possible. If your deck shoes have a removable liner, regularly take them out and spray them to keep them fresh and clean.
From a fashion standpoint, boat shoes would likely be categorized and sport-casual. These types of footwear are likely not going to be seen running around the office; penny loafers or dress shoes are the norm there. You may more likely find a pair of boat shoes under the table on an outdoor patio on someone sipping ice tea at the tennis club. Perhaps by a young fellow in pastel shorts strolling along a sunny beach someplace.
When buying any shoe, always try on both feet and walk around the store a little bit. For a deck shoe, see if you can get off the carpet and stand on a hard surfaced floor. Plant your feet and test the grip. See how the traction feels under your feet. Make sure the shoes are comfortable and stable without being too tight.