First of all, did you contact the person you bought the mohair from to see if she would replace it for you? I know that most of us will do that, or just give you a refund if you are not happy.
Secondly, if you want to get VM out of mohair, the best way is to comb it after washing. It will remove virtually all stuff you don't want, and you now have combed top, which is super easy to spin.
I raise colored angora goats. They are not covered because they are free to forage in our woods and pastures, so they do have some vm when I shear them. However, I do not sell raw mohair at all, only mohair I have picked through thoroughly and washed. VM is going to happen unless you are either coating the animals or raise them on a dry lot. If I sell mohair locks that are intact, I let people know that there may be some vegetative matter within the tight locks - if you remove the little bits, you lose the lock formation - and depending on what someone's purposes are, that might not be what they want to do.
I have seen Namaste Farms videos, and Natalie does a great job with her animals. However, she has huge expenses because her sheep and goats are raised on a dry lot - no grass, therefore, no vegetative matter. She has to ship in everything they eat, I cannot imagine how difficult that must be. She also has very high water costs, being in the desert in California. She has very fine quality fiber and you will pay a dear price for it, well worth it for those with enough money. Not everyone has that kind of money to spend on a hobby.
However, you can get great mohair from people who allow their animals to graze in pastures and in the woods. There are groups in Facebook where mohair is sold by the grower, and there are some incredibly beautiful fleeces there. These people would not be selling all the time if the fleeces were not up to par.
It is possible to buy very good fiber on-line at reasonable prices. Before you buy, ask what the seller's return policies are.
As for asking for samples, I no longer mail anyone free samples because I found that doll makers were scamming a lot of mohair producers and getting just enough free mohair to root hair on a doll with, and frankly, most of us can't afford to lose money like that.
Hope this helps to give you a slightly different perspective on your issue.