Use of a single sentence for --reason is an anti-pattern. The reasons for vouches are more important than the vouch themselves, as it gives context to the reader to whether the vouch is valuable or not. You'll see this when you look at other reputational review systems of humans. If there's very shallow vouch reasons (or none at all) it quickly leads to gaming of the system and fraudulent social credit increases. If there's rich vouch reasons, it's much harder to game the system, and easier for other members of the network to avoid fraudulent vouches.
The reason input should require a text field at least 5 lines long and 80 chars wide. This will influence the user to try to fill the box and provide more reason content, which results in higher quality signals.
Trust is a core security mechanism that the entire world depends on. It must be taken seriously and treated carefully.