They certainly seem to be an establishment that boasts large plate glass windows - they can certainly see you coming
Best thing to do with any watch you fancy is to google the model number - Casio GW-3000B-1AER as a not quite random example. This was a watch I spent a fair amount of time researching prior to buying as it was my first G-Shock for maybe 18 years.
The results allowed me to compare prices and vendors from amazon then find reviews. I also looked on eBay to see what the sellers prices were - always factoring in the p+p of course, it can vary from FREE to excessively expensive. Many of the stores have customer comments rating their service as well, always useful. In the end I bought from TikTox who also do a good line in spare bezels and straps, a decent firm to deal with as well as offering a good discount. Limited range though.
Of course, when the watch arrived it seemed too good for everyday wear so I got a cheap solar atomic new off eBay as a daily driver. My google research also pointed me in the direction of various watch forums, some vast, some very US-centric and one which seemed to fit my needs ...
It's worth considering buying from the reputable vendors from abroad - we can always tell you if they are good or bad. I have had good value and excellent service for both new and used G-Shocks from sellers in Japan, Hong Kong, Singapore, Germany and Israel as well as the UK, the only disappointment in time taken to arrive was a new black and gold hypercomplex from the States.
Ah, yes - buy a G-Shock, then one to save the "nice" one from daily damage and soon you find yourself with 41 of them with the obligatory one in the post. My dressing decisons are easy - black for office, orange hi-viz for site, ex-army gear for weekends. But I have the fun each day of deciding which watch wants to leave the shelf for the day's trip out ...