Never had a problem.
For me though, I only order stuff directly from them. I have never tried buying stuff from their Amazon Marketplace (which are resellers). These products usually cost a lot more than direct from Amazon, and can be in used condition. It's like buying from a guy at a flea market. May be good, may be crap. These resellers also charge shipping fees, while buying Amazon directly you get free shipping if you hit the threshold (is it still $39???).
Just do the free shipping option (assuming you hit the minimum order). Shipping is so fast, there is ZERO reason to pay for faster shipping.
One of the main Amazon distribution hubs is in the GTA. I've received orders at my door in 2 days just using their free option (and I did my order on a Saturday, got it Mon morn, so it shows they work and process things on weekends too). Perhaps if someone lived 1,000 km away in a rural area, it may be worth spending money on faster shipping, but there is no advantage if you are in the GTA hub.