it depends on the products which you will be advertising, i think the basic thing to remember is if your selling a product which costs below £10, the maximum you should spend on your advertising is probably £2 pounds, you get the point, its really hard to say because there are lots of companies that have TOS which are different.
you would probably first do commission + x amount of sales vs advertising fees for any given product, so lets assume a product costs $150 pounds and sales at the rate of 3 as stated in the commission index 3 is the number of sales you need to sell in order for payout of £50 ,so your commission as it stats in the TOS is £50 for x amounts of sales, you would spend £10 the max
side note, this is top of my head which i never actually done something like this but in practice its very much possible you just have to play it smart and do research
but do not smile yet i assume the user actually buys 3 products, if the user does not buy the products you get nothing back so, you see little trouble, that's why i said research what people buy online
and not to mention that the cookie also expires or the user simply deletes the cookies and user buys products but because of user deletes cookie you get nothing in return and you just wasted money phew my head hurts
