I have used Limbs to order from. Currently I am getting lists from about a 1/2 dozen people I ordered from. Many have lists they send out and are very good to deal with. Some only advertise occasionally then send out lists. Some advertise every week. I have never had an issue with any I have dealt with. Many give very nice stamps usually they are their doubles. They are just some of us selling extras to fuel our crazy need for more stamps. If you need a few names let me know not sure if I can post here because I don't have 50 posts yet to PM me.
Just a couple of weeks ago I found a UK 1840 Penny Black in a large box of kiloware I bought at an auction. There was also a pair of 1841 Two-pence blues, and a bunch of other good stuff, although the majority of it was junk from the 1970s.
It really pays to go through stuff stamp by stamp, even when it doesnt look like a very promising lot.
I got a kiloware lot in the 70s that was mostly Canadian definitives from 1967-73. Disappointed with the variety until I began to look at the variations and when I hit it with a UV light I went nuts. Tagging errors, rare hibrite varieties. The collection is in two binders now.
Generally I think the right approach to kiloware is the same as gold miners use -- the guy who spends all his time looking for the huge nugget is going to get nowhere, but if the patiently tot up all the bits and bobs you can get a worthwhile haul. Having said that, like with gold, you cant pan just anywhere.