Earlier quoted context omitted.
Also, you can't just pull tweets from the web and show them as testimonials. You will need to ask the sender for permission. (I would personally hate it if my tweets were pulled out of context and used like this for commercial purposes, without my consent.)
But does Shoutout ask the OP for permission to display the tweet? I've never heard this "you can't just pull tweets from the web.." twitter provides the embed capability, and doesn't mention anything in their terms (from what I can find) about asking for OP permission. This strikes me as something that took longer to build as a service, than it would take an individual to build for their own app.
Social proof is given in the first place by people to people whose work or service made a positive impression on them.
We focus to showcase that and leave the rest.