Q1:
1$ items are locked to everyone except a few people automatically, they implemented it a couple years back when a Torn-hosted black friday event was ruined by script kiddies buying everything up within a second or two, so now each item is locked to the last 2 digits of your ID (every 1$ item stack has a 1% chance to be unlocked for each player)
Q2:
Traders make money by being patient, having more eyes on their selling channels, and better knowledge to protect themselves - there's a couple reasons to use a trader over the higher profits for yourself:
- items that don't sell fast (like candles in your example), you may need liquid right away to buy more important items for your own progression (BBs, xans, points, gear ...) - if an item is going to take 6 months to sell and you're only getting an extra couple hundred bucks out of it by doing so, its not worth it for most players
- big ticket items like SEs, high end gear, or even FHCs and DPs make you a buy mug target, if you're not careful or forget about them after you list them you may get buy mugged and basically lose more than you would have selling to a trader
- More common items (like flushies, as an example) are sold much closer to bazaar rate, meaning you'll lose more in item market taxes than you would selling to a trader who can make their bazaar much more visible via bulk selling (esp with the new directory) - so unless you go out and promote your bazaar somehow for people to buy your 29 panda plushies, its going to be difficult to sell tax-free nowadays