Re Sams it will be 4 (sometimes 2) per membership... but after a period of time your membership will be reset to allow you to purchase additional. But (so far as I have experienced ) there is no predictability or consistency to the timing on that process. Someone on this board noted that they had had success NOT buying the max quantity at one time and then being permitted to continue buying one at a time surpassing the limit. I haven't tried this myself, so YMMV. Discover card will transact 5% on DGCs at Sams through June. Every year I consider whether I should even keep mine, and every year I do just for that one single purpose
