He doesn't.

"Like you won't be uppin' the price for another go with this slut." accused Borgin.

"Heh. Maybe, maybe not." chuckled Frank. "How much you got left?"

"More than I'm willing to spend on a filthy whore." retorted Borgin.

"Is that all yer' gripin' 'bout? Come off it!"

Despite most of her vision being blocked, Harry was able to sense a wand being pointed at her and tried to throw herself out of the way.

[Obey men!]

However the previous command of not moving was still in effect. Perhaps that was for the best as despite her war-born reflexes, the spell that Frank cast was a basic Cleaning Charm that wiped away the sticky mess and felt like her face was being vigorously scrubbed by half-a-dozen sponges. He did a rather clumsy twirl of his wand that nearly saw the implement slipping from his grip. Harry gasped as she felt her shirt start to constrict and become two sizes smaller.

"Shite."

Borgin rolled his eyes and pulled out his own wand, using a non-verbal Counter that stopped the shirt from shrinking. He looked at Frank. "Yer' a good pimp, but still a shite wizard I see."

"Fuck off!" spat Frank, his face turning red with shame.

"What were you even try'n to do? Make her tits blow apart her shirt?"

"I was tryin' to make the shirt bigger! No sense in having a whore wear trousers of all things!" His wand flicked to the side and before she could even try and protest, he pointed to her discarded male trousers and (poorly) incanted: "[In-cendier!]"

Her trousers stood up on their own, pants crawling up on the outside of it before it took off running down the street.

"...I meant ta' do that." said Frank quietly.

"...I'm sure." replied Borgin dryly before pushing aside Frank's wand hand. "Let me take care of this then, so long as you give me a discount the next time I come. [Engorgio.]."

Before Frank could even agree, Borgin had already cast the Enlargement Charm and Harry's shirt returned back to its normal proportions and then kept going until it billowed outwards into a knee-length pseudo-dress. Borgin hummed and made two slashing movements that opened up her collar and revealed a generous view of her cleavage before he nodded.

"Until next time, Frank." he said, not looking at the man and instead roving his eyes hungrily over Harry's form. He smiled creepily at her before departing with a nod.

"...Did he used to work with Madame Malkin or somefin'?" muttered Frank as he watched the man leave. Shaking his head, Frank looked at Harry and barked, "Well? What are you waitin' for? Get up! Day's still young and I need to introduce you to your new roommate."

'My new...roommate?'

Frank didn't say anything of substance after that and simply led Harry towards a dilapidated apartment complex with a rather dizzying staircase lacking any sort of guard-rails. Rather than climb it, the stairs acted as a sort of magical escalator that stopped passengers from falling off via a powerful Sticking Charm and sang an off-season rendition of various Christmas Carols. It was the kind of weirdness that Harry normally loved about the magical world but was quickly driven to the back of her mind when she saw who her new roommate was when Frank opened a door on the fourth floor.

"Oh! Hey, Daddy!"