In D&D, Craft: X is what you use when you "I'm gonna make something" whereas Profession: X is what you use when you say "I'm gonna go do X."
What this means is that if you wanted to get a sword from lumps of metal, you'd go to someone with Craft: Weapons & Armor. But if your sword just needed a tuneup, or your horses needed to be reshod, you'd go to someone with Profession: Blacksmith.
Now, obviously there's a lot of overlap (especially depending on the DM!).
And trapmaking in D&D is a little ... wonkey because of how the craft rules are set down. How long it takes to make something is directly related to the value of the end result (and, of course, your revelant skill modifiers). This means that it takes the same amount of time to make a solid gold amorphus blob paperweight that uses 200 gold worth of ... well... gold as it does to make an ornate candlestick holder that will be worth 200 gold in the end.
Strangely, they use the same value of raw materials, too.
What this means for trap making is that to make
Razor-Wire across Hallway
CR 1; mechanical; location trigger; no reset; Atk +10 melee (2d6, wire); multiple targets (first target in each of two adjacent 5-ft. squares); Search DC 22; Disable Device DC 15. Market Price: 400 gp.
You have to use the craft rules --
1. Find the item’s price. Put the price in silver pieces (1 gp = 10 sp).
2. Find the DC from the table below.
3. Pay one-third of the item’s price for the cost of raw materials.
4. Make an appropriate Craft check representing one week’s work. If the check succeeds, multiply your check result by the DC. If the result × the DC equals the price of the item in sp, then you have completed the item. (If the result × the DC equals double or triple the price of the item in silver pieces, then you’ve completed the task in one-half or one-third of the time. Other multiples of the DC reduce the time in the same manner.) If the result × the DC doesn’t equal the price, then it represents the progress you’ve made this week. Record the result and make a new Craft check for the next week. Each week, you make more progress until your total reaches the price of the item in silver pieces.
So the DC is 20 (for being a trap with a CR of 1-3), the materials to make the trap cost 133g, 3s, 3c. Assume you have a Craft: Traps with a total +10 modifier, this means you can actually take 10 and actually succeed at the check, so no randomization Yay! So you make the DC20 craft check and make ... (DC 20 x roll 20 ) 400 silver worth of progress on that trap that week. Out of 1333 silver. Give it another 3 weeks, and you'll have managed to string a bit of barbed wire across a hallway...
Also, for some reason, it's a DC 15 check to see if you're able to successfully use wire cutters on said piece of barbed wire...
==========
What this means is thus: Please discuss the insanity of D&D's craft rules with your DM before you decide to be a trapper.