So I have this childhood friend. She also lived in the US back when I was there, and then she moved to Australia, and then she moved back to Taiwan after university. She entered the design industry, where she's been working ever since.
We lost contact after she moved away from the US, but thanks to the wonders of the Internet, we reconnected around the time she moved back to Taiwan. I also returned to Taiwan a few years later, where I studied English literature, translation, and interpretation.
Her job at her workplace involves working with English a lot. For example, she needs to coordinate with overseas suppliers and clients, and organize international exhibitions, stuff like that. Presumably she was given this role because she's lived abroad for many years, and so she had a native-level grasp of English.
Keyword is "had". Soon after I moved back to Taiwan, about 13 years ago, she messaged me to say she's not sure if she phrased a particularly delicate email correctly, so she asked if I could proofread it for her. So I looked at it, and made some edits, and sent it back to her. Then, every now and then (like once every week or two) she'd ask me to proofread emails that had to be written perfectly. I was happy to do it, because she's an old friend, and because they're just short emails and so didn't take me a lot of time, and because I like showing off my linguistic prowess.
However, over the course of the last 13 years, the volume of proofreading has increased gradually yet significantly. Where I used to only get a proofreading request every week or two, nowadays I get several a day. I pretty much proofread every outgoing email she writes. She now needs me to do this, because in the decade-plus of having me as a crutch, her English ability has deteriorated to unusable levels. Like nowadays I'll read the emails she writes, and have to ask her for several clarifications before I can understand what she's trying to express. The variety of documents I'm proofreading for her has also increased. I've been looking at product descriptions, and website translations, and tourist handbooks, and press releases... I've also bailed her out of quite a few tight spots over the years, like when an overseas supplier was angry about something, and I wrote an email that was so beautifully phrased it actually completely mollified the supplier.
But it wasn't until a few days ago, when she sent me an entire multi-paged contract and asked me to proofread it, that I finally realized how messed up this is. I've been providing proofreading and editing services for over a decade, all for free, and it's been gradually escalating to the point where I'm spending significant amounts of time to basically do a good chunk of her job for her.
Problem is, though, we're kinda stuck in this arrangement now. I don't want to stop proofreading for her, because her job requires her to have a good standard of English ability. That's why she's asked to liaison with overseas contacts. If I stop proofreading and editing for her, there's a very real possibility she'll lose her job. I don't want that, she's a good friend and a nice person. I suppose I could start charging her money, but I'm kinda reluctant to do that, because that turns our friendly relationship into a business relationship. Also, if I start charging money, then I'd have to maintain a certain standard of quality; the contracts I edit would need to be watertight, instead of the "hey I'm doing this as a favor" standard of quality that's provided now. And furthermore, this might sound a bit odd, but I kinda feel guilty about being a major cause of her deteriorating English. It's like, "if I hadn't been helping her so much, she wouldn't be in this situation, so I have to keep helping her now."
So, the lesson here is... don't give a mouse a cookie.