Well, I don't post very often and I not a donor, so I don't feel I can comment on the decision to let this service through, I do however buy services on here.
This has the be the craziest businessmodel/pitch I've seen. So you have high quality service, that's great. You only have a 30% markup, that's great too. The problem is you are asking people to "trust" that your services are quality and offer no real proof. I can easily throw together a salespage about how "the game has changed!", charge a membership fee to the marks and outsource to fiverr as well.
Now don't get me wrong, if you were able to show any benefit of giving you $100 to use the sources you contract with I would be all over it. Say, for example, you contracted with a service provider on here. On their sales thread they charge $200 but through your "service" I could get itfor $150, great. Instead, the only actual pricing you talk about is a discount on writing from $3.50 to $2.50 per 100 words. I am not cheap, and know you get what you pay for, but unless you dug up Hemingway, I fail to see how a $12.50 500 word article is a discount. With your 30% mark-up that writer is making $8.75 for a 500 word article. Hell, I can write a great article in about 20 minutes. I'll charge you $8.50 for 500 words, quit IM and write for you full time- $25.50 an hour is pretty decent. Even better - pay my content club "membership fee" of $100 a month and I'll write thearticles for $8.49, but I wont send you a writing sample first.
Now I hate posts that flame and offer no real help, it's useless and negative. You don't know me from Adam, and I have a low post count, but here is my advice anyways -
There is a gap that could be filled by new "quality" service providers now. Why not just offer your services without the membership fee at a higher mark-up. If they are good, people are going to buy them, plain and simple. I understand the $100 a month would give you a stable flow of recurring income and that's what we are all after. You could offer the customers that are using you services in high volume this discount membership plan.
If you target is people who are spending a decent amount of money on SEO (and judging from the price of your writers, I'm assuming it is) then I think you missed the mark with your sales page. When I read your page I expected to see either A: great prices on your services or B: an easy to use "one stopshop" for my SEO. I would pay $100 (a lot more actually) todeal with one person/site for everything.
I apologize if you take offense to anything I said, that was not my intention.
edit: I had the price per 100 words at 2.60, it looks like it's actually $2.50.