IMO these are the most important things to check when buying an account on this forum:
1-it's not hacked, Ask to sign a message from an old address.
2-it doesn't have a pending loan, check recent posts and the loaning forum for anything related to the username.
3-it doesn't have any negative trusts even the untrusted feedback.
4-it isn't involved in anything controversial (again by recent posts and search/looking around), it may receive negative trust later if it was involved in anything controversial.