Minesweeper:
Do the following:
1. If you don't have one, go and buy a shop style wet/dry vaccuum cleaner.
2. Phone your local carpet cleaning contractors and find out which of the places listed in your phone directory under "Janitorial Equipment & Supplies" have staff that are more knowledgeable about carpet cleaning.
3. Go to that (or those) places and ask to buy a "spotting solution" (the term might vary from country to country) for removing biro from a carpet.
You see, the companies that make the carpet detergents, enzymes, defoamers and acid rinses that professional carpet cleaning contractors use to clean carpets with will also offer a line of stain removers. Typically, they will market these stain removers as a kit containing anywhere from 8 to 18 different chemicals for removing different kinds of stains from carpet and upholstery. However, they also will sell these cleaners individually because if a contractor runs out of one, he doesn't want to buy a whole kit of 18 just to get more of the one he needs.
Those Janitorial Supply places typically sell to contractors, but they will also sell to you if you pay cash. The reason why is that there's no such thing as a Janitorial Supply retail store that they also sell to who'll bark at them for stealing their retail business. The closest thing to that are the grocery and hardware stores, and those places don't buy from the local Janitorial Supply outlets anyhow.
Tell the guy at the place you buy the biro cleaner from that you have a wet/dry vaccuum cleaner and intend to use that as a poor man's carpet "extractor" or "shampoo'er" by just pressing the suction end of the vaccuum hose directly onto the carpet pile. (He'll realize that's a good idea for someone wanting to remove a stain from a carpet).
Follow the directions on the bottle. Most likely you'll just apply the cleaning solution to the carpet, work it in, allow time for it to work, and then suck the soiled cleaning solution out with the wet/dry vaccuum cleaner. Repeat as necessary. Then, do an encore performance using clean rinse water.
And, the above advice also applies for any other kind of a stain as well. You can get "spotting solutions" (which is what they're called here) to remove ink and toner, coffee and tea, blood, feces, urine, vomit, you name it. And, with a cheap wet/dry vaccuum cleaner, you can use the same cleaners the professional carpet cleaners in your area use to remove stains as well as they could. Certainly it would be cumbersome to shampoo an entire carpet with a wet/dry vaccuum cleaner, but you can certainly use a wet/dry vaccuum cleaner and professional cleaning products to remove stains from it. Ditto for upholstery.
PS:
I think the only reason why more people don't buy their cleaning supplies from janitorial supply outlets is because they're simply not aware that by doing so the will come into contact with people that are highly knowledgeable about cleaning willing to give out free advice on cleaning in those places.