I had good experience with them, you just need to know how to choose. and in doubt, don't buy it, coz you will lose it. you are paying the price of a civic for a ferrari, do you expect it's gonna run perfect? most of the livestock there need a lot of TLC, but for the price, you are not gonna lose an arm or a leg even if they don't make it. once in a while, they do have rare and unique species that you only find in a public aquariums. so it's really worth the money and the trip to see if you can score.
always look for the sign: chewed up fin, shortness of breath, colored dots on the skin, are they active, etc. also add a little luck in there too. again always quarantine and remember, you get what you pay for. good luck