Fellow author @Nyhterides recently posted about artists constantly hounding them for commissions. I am totally on board with their views on the subject.
I've also experienced this plague, and one appeared on my A03 account last night. It was the straw that broke the camel's back.
This is the response I sent back: -
As a writer, I always hope for readers to become invested in my storytelling, to enjoy the journey with my characters and plots, and, hopefully, they'll engage in pleasantries and, perhaps, offer some constructive criticism. Knowing I've created something they enjoy and eagerly anticipate reading brings me joy.
But when someone comes along, reads one chapter - IF THAT - then starts discussing commission work, well, that really annoys me.
I'm fed up with the plague of artists touting for business in this way. When I need covers created, I either make my own or visit a site where registered artists showcase their work, allowing me to read reviews from their customers.
So, no, I'd rather not discuss cover ideas with you, but I sincerely wish you success with your art. Take the time to research potential clients by reading their profiles; mine, for example, explicitly states that I do not appreciate being harassed by artists touting for business. Alienating potential clients is not recommended. If Ao3 do not permit you to create your own profile with samples of your work, corresponding reviews and price ranges, then register with Fivver, or a similar platform. Trust me, when writers want such a service, they will find you.