You'll find plenty warnings about SanDisk cards, although to be fair some people use them in some cams with no problems. There are safer choices.
As to GearBest I've bought from them several times, but they screwed up my last order. I can use what I got and it's not worth the hassle of doing a return. Otherwise they're OK to do business with as long as your expectations are low. Just another Mega-Store from China with innacurate listings, slow shipping, poor customer service, crappy warranty service, occasional shipping mistakes, but sometimes crazy low prices. Always use Paypal, as that is the only real leverage you have against problems. Something of a gamble but usually OK. From what I've seen GB seems to be declining recently compared to the other MegaStores with more sales of out-of-stock items, wrong items sent, and more hassle regarding returns. For now I'll still buy lower-priced stuff there but if they get much worse I'll probably end that.
You don't get what you don't pay for and with MegaStore's prices all you can really expect is to get the listed item eventually. If you want more go elsewhere.
Phil