Chances are you've got some character (or toon as some like to call it) with a crafting profession. Chances are even higher that you've had to deal with someone elses crafting profession to get an item you needed, because very few people are completely self-sustaining when it comes to crafts i.e have at least one character with every profession (I'm soon there though, just gotta finish bs on my warrior.) And even if you do have every profession at your disposal, you might not have all the patterns out there needed!
And if you ever try to get someone else to craft items for you, or do something else for you like open a lockbox or port you somewhere, you'll notice that it often comes with a fee. These fees are often set around a standard, for instance the opening of lockboxes usually costs nothing while getting a gem cut costs somewhere around 10-15g. Where do these standards come from and what is really a reasonable fee to ask for?
The simplest answer would of course be to simply ask for whatever price you like. If people don't pay, they no get. You could do that of course, but you sure as heck won't make much money from it, unless you happen to be the only one who can craft that particular item, more about that a little further down. So what is a reasonable price if you actually intend to make some money from something?
First of all it is important to know that not all crafting professions are much asked for. Some like engineering are nearly never wanted, while others like enchanting or jewelcrafting are asked for every 5 minutes in trade. Yet again others like inscription are highly wanted but rarely asked for. The reason for this are connected to the properties of the goods that the professions produce. Glyphs are cheap to produce and often used in big quantities at a time, therefore it is best to sell them through the AH. Gems on the other hand are medium expensive to produce and used in a medium quantity (by the market) and are therefore sold both at AH and through trade. Enchants on the other hand are usually very expensive to produce, and often the demands are very select. Therefore they are mostly sold on demand only, and not so much through AH. Others yet (while not crafting professions) are of course only usable when demanded, such as portals, the opening of lockboxes or boosts.
So the cost to produce something, and the risk of producing it beforehand (when not knowing for sure if it will sell or not) will affect the prices some, and also decide whether it will be sold on AH or if you have to yell for a crafter in trade.
As mentioned before, exclusivity will highly influence the prices of an item. If you can craft something alot of other people can craft, you won't be able to ask alot of money for doing it, since anyone else could jump in and do it cheaper. There are even people who do stuff for free, so watch out! If you happen to be one of very few to know a particular craft, like say some of the vanilla enchants that only drop in raids such as MC, or like when the Glyph Mastery books were first released on the market, you'll be able to demand a very high price for your craft. This is the case if a pattern/recipe is either time consuming or expensive to get, since those factors will greatly limit the amount of people who know it.
And one last thing that will affect the prices are the effort the crafter has to put into something to produce it for you. If you provide the crafter with all the mats you only demand about 5 minutes of his life, and this factor won't count for much. But if you want to buy an item ready and made, it is reasonable to expect to pay for the time the crafter has put into getting those mats together.
For instance, the other day I bought some 4-5 pieces of the Tempered Saronite set all ready and crafted, paying a little more for each item than I would've if I had collected the items myself. Since I didn't have to go through all the hazzle of collecting the mats myself, I paid him a little extra for doing it for me. It doesn't really matter if he happened to get the mats really cheap or really easy, you have to use whatever effort you would've had to put into it as a base. I wrote some about this some posts ago.
So the reason most people don't use a fee for opening lockboxes is because it didn't cost them anything to skill their lp. I think the main reason however is simply that whatever's in the box rarely would be worth more than any fee you might pay, which would effectively end the necessity of opening lockboxes at all.
The reason you pay some 5-10g for a mage portal is usually because that is what the mage think his time is worth, although the actual item they use costs about 20s or so (40s perhaps).
The fees for other crafts like gems, enchants, tailoring and so on is usually a mix of making it worth the crafters time and repaying some of the immense amount of money he/she put into learning your particular craft (although your craft might've been "free", i.e from the trainer, any crafting profession still cost alot to skill up).
The fee you pay for crafts such as glyphs is based around the very simple "supply and demand". Glyphs high in demand are usually expensive simply because people pay for them. Glyphs low in demand are cheap because no one wants them.
So to conclude, here is a list to check before deciding your price;
- What amount of demand is there on your item? high/low?
- What amount of supply is there on your item? high/low?
- How much effort do you have to put into producing it? high/low?
- How much effort have you had to put into learning it? high/low?
The top two, supply and demand, are usually the ones that matter most, as in any market.
Maybe this has given you a little more insight around the working of crafting professions, so that you can understand the WoW-market better and profit more from it!