So while loading the game a dark elf, with the DB outfit and two daedric daggers, decided to appear on my screen. As the Listener I want those daggers but I'm not to keen on investing/wasting perks in smithing. So my question is this: Can you buy daedric daggers from any merchants/vendors?

Perks in smithing aren't wasted.

Yeah you can buy them from the women in the tavern in riften, where the thieves guild is located. She will sell daedric daggers and bows at high levels.

You can also craft daedric daggers using the forge under the college at winterhold (with no smithing perks), you need to do the 100 skill conjuration quest though.

Well, for me it's wasting since it doesn't fit with my playstyle/character. Any idea at which level she starts selling? Thank for the answer btw!

With smithing, you can get them around lvl 10 if you really really want to.

Otherwise, you'll have to wait until at least lvl 50 (in my experience) before daedric stuff has a chance to show up in stores.

You will need to be a high level to buy them (50+), have level 100 conjuration for the conjuration quest, or smithing 90 with the perk to craft. They won't be that strong without smithing though tbh.

I know, but then I will have to spend 4-5 perks to get the option to smith deadra stuff. Those perks I need on my one-handed skills unless my assassin will only use bow and sneak attacks for the rest of his (virtual) life.

Use it to outfit your followers, or make gold on smithing and selling stuff.

If your a warrior or thief class that wants either Daedric or Dragon Armor then you should get smithing. But in my case, since I'm a mage, I only upgraded the perk Steel smithing and arcane smithing which is enough for me to level up my smithing and upgraded enchanted armors that I've looted or created.

I don't want the armor, just the daggers. Because they look cool, lol.

After lvl 35 daedric weapons start to appear more common in chests. After lvl 40 finding them in chests is as common as finding ebony or glass stuff. That's my experience about it. But I have never seen anyone to sell them. I personally dislike the look of daedric items so I don't use them and I don't have perk to smith them.

As stated, you can buy them. With Smithing at 100 (no perks) and store-bought +Smithing gear and potions, they can be quite strong — I'd say somewhere around 50 base damage with the aforementioned benefits and like 3 +20% perks in one-handed. That's 1,500 backstab damage with the perk and the gloves, not counting enchantments, poisons or the added damage bonus for power-attacking.