This includes native English writers as well as those who have English as their second, third... etc, language. Expectations may be lower on the latter group but more than a few natives produce paid content that is barely on the level of the XX-language writers. Yes, you will get loads of crap from many non-natives but it is also surprisingly easy to find those that do deliver perfectly good, sometimes great articles. The same price point may often deliver the goods from those you least expect it.
This is the main reason why the market has become so competitive for many native English writers.
You are not delivering.
If you expect the buyer to come back and pay for your native services again you need to deliver more than just words. Correct English is of course a given and not hard to supply, but there has to be some meat and bones, some structure and flow, perhaps even a hint of a voice. Words are not enough. Anyone who is ok with grammar and using Open Office will produce a article without spelling errors. But is it good? Is the content coherent? Does it speak to the reader? At least a little bit? To be worth more than the non-native rate, it needs to.
You get what you pay for.. or at least that is what a buyer hopes for, and if you hype your stuff it better deliver or someone else will grab the jobs next time. Luckily, there are several.. quite many actually.. content writers from both camps on WF that produce great stuff and they are hopefully reaping the profits from their well-done work.
To those who feel the cold breeze of competition - take a break from your own writing and buy a bunch of articles on similar subjects within your own price range, and check out what you are up against.
You may find that many are delivering below your own writing. Ok, then perhaps you should increase your rate and make a stand for the quality that you deliver.
Or you may find that you are on the same level, or perhaps below, the quality of competition in your price range. Ok, then you have 2 options: Keep the price and raise your quality in order to supply that which is expected of you. Or, face the fact that you may not be worth every penny, deflate the ego and settle on a price point that is somewhat lower but that may bring you more business from that customer segment.
To those buying content. I suggest you go on a test-run now and then. It will keep your writers on their toes and you may perhaps find some of the golden nuggets that are out there.
To the many writers out there who do Write Good Stuff, take pride in the fact that your craft is good.