I would give this a very quick read if I were you.
Then search the forums and media channels.
Then calm down, have a bit of a think, and contact me with details of the problem.

The game won't work.

Check your computer is compatible. Almost any PC, Mac or Linux from 2012 with minimum specs should run my games. Sometimes you might need to enable a 32bit mode or download the 64bit version. Although having a bit more than minimum memory tends to help matters. Also, try switching your computer off and then on again.

My computer just refuses to run the game.

Perhaps your computer is tailoring your leisure and/or hindering fun time for a reason. If your computer has become self-aware please disconnect it from the internet immediately.

Is my computer too new/your game too old?

One day perhaps. At time of writing final builds should be compatible for years. However, one day I/someone will have make new builds or emulate current operating systems for existing builds of my games.

My hard drive is going bananas.

Your hard drive is very sick and/or some system process is being a space shuffler/space hog. My games load it all once, with occasional preferences writing and the odd music file streaming. Any issues are symptomatic of a problem with your computer that my games are merely stuck in the middle of.

My screen's aspect ratio is not supported.

A deliberate choice on my part that my games target a 16:9 ratio (it's the most common these days). Some games have an early startup option (enabled by holding Option on launch). From there you can hopefully choose a screen/window that's right for you.

Something weird happens when switching fullscreen to windowed.

It's a Unity thing. I'm slowly improving the visual options to be more fluid and also hoping that Unity will develop a fix to allow easy graphical options, but be patient. I advise doing your settings once and leaving them alone (for all video games, not just mine).

There's flickering...

Your graphics card is not having a good day. Yes, it really is your graphics card.

Key rebinds won't accept controller commands.

That's correct. It's called Key rebind not Controller rebind.

You game doesn't work with my keyboard type.

All my games use KeyCodes which utilise the standard inputs for Western keyboards, regardless of language or keymapping. Your keyboard and computer need to sit down and have some interface guidance therapy. Then try my game again.

I want a refund.

Then get one through the online store, if they offer it. I do not refund directly.

I got charged a sales tax/VAT/something extra.

That's down to the online store, your country, and whatever arrangement is in place between that store and your country. Contact the online store to found out what happened and why (you should have been made aware of any taxes BEFORE you agreed to purchase).

The price of your games changes (daily).

I set the price in GBP (Pounds Sterling). The rest is the fault of the foreign currency exchange markets.

I bought a version of a game for one system, do I have to buy it again to play it on a different system?

In terms of DRM, no you do not have to buy it twice. There is no DRM. The executables are not locked (preferences are NOT stored in the same location). In terms of getting a different version for a different operating system, go through the online store to see what's available (there should be many versions available for one purchase).