Jomashop is a grey market seller. When you buy from them you will not get the original authenticity papers that come with Swiss watches. The original manufacturer warranty is not valid without this paperwork/proof of authenticity. Jomashop will match the manufacturer warranty, but they are the ones that will have it serviced during the warranty period. You may still have the watch serviced by the brand (Cartier for example) during the warranty period, but you will have to pay for any service.
You can do better than Jomashop on price. My AD that sells Cartier will discount deeply.... Of course the guy tells you no one will discount...he wants you to buy from him.
Look on TRF, TimeZOne, WatchNet etc...great deals and very reputable long time sellers.
If you want the best possible deal, then look for a sweet pre-owned piece...but only buy if you get the box and papers,,,,cuz if you choose to resell the watch, new buyer will want a HUGE discount if you dont have the Authenticity papers..... I would never buy a GEN without Authenticity papers, but thats just me.
Which Cartier are you interested in....happy to point you in the right direction if you want.
Good luck