I work close to a thrift shop and I like to go for a walk each day. It was way too hot for a walk today so I decided to check out the thrift shop. It is large so I could do some walking and perhaps snag a deal.
With my phone in hand I looked at items and found a water filter. I looked it up on Ebay and they were selling for $50 - $60. I bought it for $3 and posted it on ebay and went to work.
This entire process took me 20 minutes.
A few hours later, someone bought it for $40 on ebay.
If you want some extra cash, head to the thrift store with your phone and see what you can find. Never go feeling like you have to get something or else you will end up with junk. Only buy things that you know have a high chance of selling for a profit.
Hope this helps