Smartphone is not worth it, most cost $80 a month plus the cost of the phone. You would have to do an awful lot of yardsaling to cover that, at least in my area. If your employer provides you with a smartphone then you are golden though.
Prices are down during the summer too, so you can't really gauge true value if you are like me and hold stuff to sell during Xmas, a game that goes for $5 during the summer might be worth $30 during Xmas season especially for modern games. System bundles go for A LOT more during Xmas than they do over the summer, so do lots of games even if they are crappy games. You can still make decent money if you buy crappy games for cheap then list them in a lot (group) during Xmas just not usually for old sports games. Sure there are games that sell equally in the summer and during Xmas but I find that with most games they do sell for more during the Xmas season.
If you can get a bunch of common games for $1 each then it might be worth it, however if its something stupid then I usually pass it up because it will not be easy to sell unless it is something I want to play myself. For example N64 games might be worth it if you can get 10-12 of them for $1 each, because that would make a nice group to sell, but unless you can get a bunch going you will be stuck with sales of $2-3 per game.
Also don't underestimate games targeted towards children, you have to keep current with these but some games go for a lot because kids want them, even if a gamer would normally consider it a bad game.