I hope you have found another LFS. At the very least, ask all questions here or find the answers in books, and go in armed with info. Don't trust them from this point on. What else do you want to put in there with 2 triggers? (what are they by the way?). Did this person say they would buy a trigger back? 2 triggers in a 90 g tank might get crowded, assuming you want other aggressive fish.
As for the algae, it is quite normal. Learn to recognize it. A cycling tank is very unstable, and lots of things "bloom" to make use of the available nutrients. We want a bacterial bloom to colonize the filters (if running a wet dry type of system). Algal blooms occur as other nutrients (like nitrate, a fertilizer) comes into play. Once the tank cycles, and these nutrients are no longer at high levels, the algae will die off. However, this slime type algae will turn up again, and is usually a good indicator of time to do a water change, check parameters, even think about how old the light bulbs are! It is a first lesson in learning to read the tank.