How we cite our quotes: (Chapter.Paragraph)
Quote #1
Howl was equally patient and polite with customers from Porthaven, but, as Michael anxiously pointed out, the trouble was that Howl did not charge these people enough. This was after Howl had listened for an hour to the reasons why a seaman's wife could not pay him a penny yet, and then promised a sea captain a wind spell for almost nothing. Howl eluded Michael's arguments by giving him a magic lesson. (6.13)
The funny thing about Howl is that he refuses to explain himself, no matter if what he is doing is good or bad. Here Howl is doing something charitable—he's giving away his magic for less than its value to people who really need it—but Michael only sees that Howl isn't bringing in enough of an income. And instead of explaining what he's doing, Howl just distracts Michael with a magic lesson.
In a way, this just adds to our sense that Howl is secretly the best guy in the novel: he doesn't boast about his good deeds, even though he appears to be doing them quite often.
Quote #2
If you knew the trouble we've had because Howl will keep falling in love like this! We've had lawsuits, and suitors with swords, and mothers with rolling pins, and fathers and uncles with cudgels. And aunts. Aunts are terrible. They go for you with hat pins. But the worst is when the girl herself finds out where Howl lives and turns up at the door, crying and miserable. Howl goes out through the back door and Calcifer and I have to deal with them all. (6.40)
Sophie believes that Howl literally eats girls' hearts, but of course that's really just a metaphor for what he actually does: he's incredibly fickle, and he likes to make girls fall in love with him… and as soon as they do, he loses interest.
This character flaw has two interesting plot functions: first it encourages Sophie to delay admitting how she feels about Howl, which keeps up the suspense of their weird, bickering relationship; and second his emotional unreliability turns out to be a symptom of his contract with Calcifer. Once Howl gets his heart back, we assume that he won't be so irresponsible and that Sophie can trust him. Howl gets to be the romantic hero of the book because Howl's ethical flaws regarding women turn out to have an explanation: after all, he can't help it.
Quote #3
Sophie thought of Howl on one knee in the orchard, posing to look as handsome as possible, and she knew they were right [that Howl is not truly in love with Lettie]. She thought of going to the bathroom and tipping all Howl's beauty spells down the toilet. But she did not quite dare. Instead, she hobbled up and fetched the blue-and-silver suit, which she spent the rest of the day cutting little blue triangles out of in order to make a patchwork sort of skirt. (9.13)
Howl's vanity is a serious factor in his love life. He always seems to think about how handsome he is and how he can look his best, as opposed to thinking about the woman he's actually talking to. The reason that we know that he and Sophie are meant to be together is because Sophie sees all of Howl's worst sides—his selfishness, his vainness, his childishness, his drama-queeny-ness—before she will actually admit that he has been kind and generous to her.