I have an app in the Google Play store, it has around 1,500 active installs and I decided to do a bit of an experiment last year by releasing a paid pro version. It was exactly the same, it just had a different colour icon and 'Pro' branding. I put the price at 99c/99p, and put a link to it in the free edition description (the descriptions were the same other than that). I was pretty surprised when people actually bought it...
I think I made about $5 before I realised after a couple of weeks, and then I took it down. The app hadn't been touched for a few years and wasn't the best quality, so I didn't feel happy for basically scamming people. I was considering doing the same for a donate version, but wanted to improve the app first - which I never got around to.
I think you could get some income by doing something similar, but it's very unlikely to replace your main income.
I don't consider it scamming to provide a paid version without extra features. There are other software products that have this, like Winrar and Cyberduck.
Additionally, if I see a "free" and "paid" version of something I think I need/want, I always get the paid version, because I don't want ads. I'd rather pay 99c~2,99c for no-ads then having those freaking annoying ads.
I want an ad-free home. No ads on my PC, TV or phone. Nowhere.
It really depends on how it was worded, if it was saying that paid version is exactly the same and is there to express your support, then it is not a scam.
I think I made about $5 before I realised after a couple of weeks, and then I took it down. The app hadn't been touched for a few years and wasn't the best quality, so I didn't feel happy for basically scamming people. I was considering doing the same for a donate version, but wanted to improve the app first - which I never got around to.
I think you could get some income by doing something similar, but it's very unlikely to replace your main income.