At the moment, it just isn't that sort of a sales site.
Your idea would probably only work with big stores that had an ebay presence or else in real life stores.
There are still a few smaller sellers & private sellers around on ebay and if it is a mum & dad seller, they just want to sell their item and move on, not hang around waiting for small payments.
I could see huge problems happening if people paid progress payments over a few weeks, only to find the seller had up and gone.
You don't find layby on Catch of the Day or other similar sites.
It sounds as if you are steering clear of credit card dependency & getting into debt. Wise move.
My advice would be-although it is hard, why not put away eg $5-$10 a week into a money box or spare purse or special bank account.
Or have an amount taken out of your pay and put in an account.
Then when you see something you like, you'll know exactly how much you have put away and whether you can afford it.
