OP, too many factors to determine what is going on. It could be that you have too many devices pulling bandwidth (Netflix is notorious for this), it could be at home you are getting interference from your router, it could be that the store had a better router than you (stay away from combo gateways, they are bad). It could be the angles in your house, the appliances, literally, a lot of things including distance if you have a large home (look into repeaters or extenders), it could be that your browser history was cluttering up the signal.
Sorry I cannot help but I want to tag along on this post....I was told this weekend by Directv that my internet is not good enough to download movies, my download speed was around 14 Mbps something and it needed to be around 15 Mbps. Top it off I think I have the best internet plan available in my Lexington hood. WTF?
I would say its a plan to sell you more speed. But you think its best plan? Usually Netflix recommends 3-5 mbps for HD, and 20+ for Ultra HD. So they could be talking about this. But you can download movies with 1 mbps, it would just take awhile. Your speed is fine for netflix, if you meant streaming and not downloading, which are different. Just be careful, as each device on your network will pull from your available bandwidth. So if you have 2/3 iphones, a tablet, a comp, and tv, you may be taking away from your streaming capabilities. You just talked to someone who was trying to make a buck off you.
Edit, netflix and sometimes devices like PS4 that contain netflix app on them will sometimes pull more bandwidth so you may nned to check your allocation settings. For example, you may need 5 mbps to stream a movie, but netflix might actually pull 15-20. You have to go into settings and adjust allocated bandwidth.