Yes i realize that you can already buy armor and potions/poisons but what if the person you go to doesnt have what you are looking for? Well you should be able to bring them the base materials (at least the ingot for smithing) and have them make what you need.
With smithing you can bring them the needed ingots, leather. leather strips ( if you find the mats in loot or smelt the ingot from the raw ore) or use the ones they have in their inventory ( though it should cost more for them to use their own mats) and get a menu similar to the actual crafting from their you can choose what you want and pay for it to be maid. There should be another service you can use that allows you to improve the weapons/armor in a similar way.
With alchemy you can bring raw ingredients to an alchemist/potion brewer and have them brew you your potions/poisons for a cost. Now with alchemy you need to know what the effects of the ingredients are, the way around this could be when you enter their crafting menu and sellect what what potion type you want (restore health, stamina, etc) you have a double section on the left of the window like you do in containers, that shows what they can make with their ingredients (which will cost more) and then below that is what you can make with yours. Because your using them to make it you can see what all the effects of an ingredient are, and be able to use the "perks" of alchemy through them, but at a price of course.
With enchanting it agitated me that the guy in the mages college would not enchant things for me. You should be able to use his services to enchant things. you can bring him the item you want enchanted and a filled soul stone ( or use one of his for a higher price) and have him enchant it for you. He should have the full enchantment list. and you should be able to adjust the strengths of the enchantment through him, but of course the stronger the enchant the the more pricey it should be.

