Gullifer is obviously secretive - he looks like he's never quite sharing his full thoughts about whatever he is talking about. With long breaks of silence and the feeling of being judged and watched sprinkled into his conversation, Gullifer comes across as thoughtful but also uncomfortable to a lot. When he's not just silently watching, he is easily humored and smiles a lot - Gullifer is an avid user of slow and gentle (but frequent and spacious) hand gesticulation and so the contrast between him actively and passively engaging in a conversation is quite apparent. Not that he seems to mind either role.
Gullifer likes other people and considers most other beings to be 'cute'. It can come off as insulting, but he means it more endearingly - much in the same way one might view cute animals. As a manipulator of fears, he seems hard to frighten. In that regard, he is very laid back.
He's an avid fan of horror and fright as entertainment and he takes enjoyment out of scaring others by sneaking up on them, though he keeps this to very light pranks and will apologise if others find it too much. For examples, he can tell strong fears and phobias and he sees it as the right thing not to take advantage and hurt others by using that. So whilst he is morally questionable in his business, he does seem to make effort in being kind company. This partially stems from his opinion that everyone is adorable and cute - you would have to be pretty sick to scare puppies for fun, when they can't understand it's merely teasing, right?
Gullifer is aware that most people whom buy fears either use it as a collectable (much like himself) or use it like a curse for someone else. He doesn't particularly mind that a lot of his clients aren't fully kind people, but he can be picky about what he sells to whom. After all, a good fear can quickly spread and get out of hand, if you don't manage it well. Paranoia is a wild beast. And frankly, Gullifer enjoys everythign to be more orderly - he loves collecting, be that fears, bottleships, clocks or other items that strikes his fancy.