wow....this LFS sounds pretty bad, no offense to you or anything = ( Honestly...they told you a tang would be ok in a 29 and then tell you that fish rarely get sick??? wtf. Telling someone fish rarely get sick is like telling someone the sun rarely gets hot. The guy may not use a QT, a lot of people dont, but I guarentee you he's had ich 90 million times. Although technically I guess ich isn't the fish getting SICK, since its a parasite and not a real deseise, but its still something that needs to be treated properly.
It sounds to me like they don't care if your tank fails miserably, they just want to take 200 bucks off you for a couple fish, then never see you again. The things they told you are the 2 worst peices of advice I've heard in a while, honestly.
OK, i've got it!!!....here's what you do:
Go back in there and ask them if that mandarin dragonet would be a good starter fish for your aquarium that you just recently set up. If they say "absolutely" or anything that sounds like "yes" or even "probably" at ALL....ignore anything else they ever tell you. A mandarin will starve to death since it only eats copepods (99% of the time) and those take MONTHS and TONS of rock (75+ lbs.) to accumulate to a level thats appropriate for them. So if the employee tells you that it would be alright, then one of 2 thigns is occuring....neither of which are good.
1. They are clueless and stupid. This is unlikely, since most people that work in pet stores have at least SOME semblence of a clue, if not from personal experience then at the VERY least they've been told what doesn't work by someone that DOES have experience.
2. They solely want your money and nothing else. This is almsot guarenteed to be the case. This is even worse than them genuinely not knowing whats right or wrong, because it means they are intentionally lying to you to literally STEAL your money. They know you're screwing yourself but dont care.
hope this helped.