How much percent of stake for someone joining startup in Marketing role

Hi there, I really need some guidance on how much stake should one give in startup for someone joining as Marketing and VC strategy role. I have no idea the one who is joining asking too much stake. Currently he is asking for 12 % stake to take responsibility of making VC fund strategy and getting VC funding and for marketing. The product has gone past MVP and we are doing domestic market launch. We are planning to collaborate now with them. Is 12% really worth. On what factors should one evaluate how much stake to be given. Is it really required for collaboration?