Taking a quick skim of my inbox, I currently have 23 sellers I'm giving repeat business to. The highest national representation is 6 of those sellers being from Indonesia. According to numbeo, a 1 bedroom apartment in the center of the national capitol (Jakarta) is about 475 USD. The individual seller I've given the highest number of orders is in the Ukraine, where a 1 bedroom apartment in the center of the national capitol (Kyiv) is about 575 USD. The individual seller I've paid the most is in Lithuania, where an apartment of that type in Vilnius is about 625 USD.
If we want an analogy, a similar apartment in Washington DC is $2325. So, it's possible, for those sellers, the impact of asking for 250/mo might be like asking an American for $1,000/mo.
I doubt those sellers would be here for me to work with if that kind of fee was there. It would instead be sellers with higher prices trying to recover the cost of the monthly fee. Likely, this would put prices outside my budget. As a result, I possibly would not be here either.
Personally, I've accepted that there's a lot of sellers which are a waste of money. I spend the money to get them to do the work and verify for sure. The upside of always rolling the dice is that I've also found a lot of excellent sellers who were sitting there at 0 reviews, 0 orders in queue, who were cutting discounts to get growth. Many of them have since gone on to increase their prices and consistently have orders in queue.
The solution to filtering bad and good, for the benefit of buyers as a whole, might be more functions which help buyers like me run this "paid audition" process more easily and cheaply. I got VID recently, and it feel kind of like it could do that, but the coupon seem to want me to make larger single orders instead of place orders with new sellers. Giving me coupons to reduce the risk of trying out new sellers would enable me to manually verify who is good and who isn't.