There are two different things to consider, crafting Gems (jewelcrafting) and equipment (blacksmithing).
Crafting a Gem does not need live streaming at all. It is simplest to find someone who has the higher level gem you want, and trade them the materials (lower gems & crafting cost) + fee/tip in exchange for the gem you want. You only need to be aware of the standard trading scams and take your time when trading. Don't expect to save 15% of course, usually the savings would be split between you and the crafter.
If the crafter doesn't already have the higher level gem at hand, you want them to stream and follow the guidelines below for crafting items.
Crafting Blacksmith Recipes:
Usually the streaming guys are more expensive.
I have spent a lot of time browsing through the Crafting forum (on bnet) and I assure you this is not the case. Of course, as with everything else there will be a wide variety of 'shops' with different prices; i.e. you can pay 300k for a HoC craft or you could spend 20 mins to search for someone who does it for tips.
- Look for a crafter with live streaming who offers their services on the battle.net forums.
- Try searching for
<item name> Free and
<item name> tips, but don't be tempted by non-streaming crafters just to avoid paying a fee.
- In their crafting thread, look for customer vouches: hopefully multiples, its fairly easy for scammers to get one or two fake vouches from other scammers
- Unless you're in a hurry, I suggest watching the stream for a few mins to double check that the crafter is legit. Also helps to get an idea of what kind of tip would be fair, but if you're poor then you can just tip like Kormac.
- Prepare the exact amount of materials (tomes, essence etc.) ready in inventory so you don't waste their time.
- Send a friend message clearly stating the item to craft and quantity (e.g. Want to craft 3 Helm of Command please)
- Side note: for some strange reason, several crafters use Inferno level games to do their crafting, so use whichever character has unlocked the furthest difficulty level (and inform them if its not Inferno)
- Especially for those doing high value items for tips, they tend to be very busy so be prepared to wait a few mins - you'll get an idea of this if you watch the stream beforehand.
- Join the game when invited, be alert for party or whisper messages to confirm item, quantity etc.
- You need to give them the materials/fees first and then they should trade you the completed items (also make sure to have enough inventory space for the complete batch)
- Once your craft is done, thank them and leave.
- Assuming everything went well, consider adding a vouch on their thread - it helps other users know they're legit.
- This is my personal opinion, but I suggest removing them from friend list if you're not planning to use their services again soon as a courtesy, since crafters often run against the max allowed and have to figure out whom to delete from the list.