I think it varies considerably according to what is scheduled and what are the personal tastes of the presenters.
Before a clothing show, the guest and presenter have a rail of clothes to be shown in the hour to choose from.
If there are back-to-back clothing shows, the presenter may end up wearing part of the outfit from one brand and part from another... especially if they can switch out one item for the second show. Generally the women presenting a fashion show have to wear the brand.
Generally it seems rare to see the really slim presenters (Jackie Kabler, Jill Franks, Pipa, Sara Griffiths, Ali Keenan) regularly wearing QVC brands.
Ali Young wearing QVC fashion is an event in itself.
The men, luckily for them, only seem to get roped in to the Christmas jumpers.
Marv regularly wears QVC fashion. Julia also. Anne Dawson tends to just wear Yong Kim or Join, or Marla Wynne, or non-QVC.
Chloe seems to avoid QVC fashion as much as possible and when she can adapts to her own style.
Jilly Halliday seems not to wear QVC fashion unless forced to by her schedule.
Catherine Huntley will for preference wear Onjenu, or will wear other fairly fitted dresses from other brands. Same with Claire Sutton.
Kathy rather has to wear QVC fashion seeing as she does her fashion show! I'd say she's the only one who is regularly dressed by a stylist. The others have only themselves to blame/congratulate.
Then there is Debbie... who seems to possess a) only QVC clothing, and b) no talent for chosing an outfit that suits her. It's pretty much a shocker if she isn't wearing QVC fashion at home or at work, judging from her attire in all the pictures she posts of herself on her own blog on QVC.
Catherine Huntley talks about QVC running through her like a stick of rock. Debbie actually walks the walk rather than just talking the talk.
Some of the presenters seem to have a natural gift for dressing well to suit their figures, with only occasional lapses into fashion disaster. I'd put Pipa, Ali Keenan and Jackie Kabler at the top of the tree for a fashion gift. I think Jilly and Anne both dress well for their bodyshapes.
Bottom of the tree without hesitation are Debbie and Ali Young. Debbie at least has the excuse that she's shopping QVC fashion. Ali Young doesn't have that excuse.