KEEP IT CLEAN!! ANIMALS HEALTHY!! AND HAVE GOOD EMPLOYEES!!
Those are the most important. ive been driven away from many places due to lack of these things.
I like tanks clean! tanks arent clean= me turning around and taking my bussiness else where. keep fish tanks nice and clear and fish nice bright and active. Also keep animals looking healthy. keep sick/ not so good looking ones in the back. this goes for fish and herps. my eyes ussually go right for those. they stick out like a sore thumb
Keep good employees on hand. i hate going into places and having employees who know NOTHING! i hate getting fed bullsh*t when they think you know nothing. it just makes me want to leave. i like going in and getting noticed right away to, makes me more apt to buy something if the help is there right away.
keep care sheets everywhere as well. employees that know there stuff are good but having tangible info is a huge plus. let people walk around and read it while they shop around. helps them come up with better questions which in the end would help with a better transaction.
I wouldnt keep alot of high end stuff on hand right off the bat. you will loose money. think about the feeding, electricity, and other expenses that will go into each animal. more cost consuming with herps than fish. keep a real good variety of beginner fish and intermediate fish. you can keep some high end fish as well. but keep more mainstream ones. keep the high ends to special order. its nice to have a place to go to who can get you what you need with a quick phone call

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ive been dealing with a little hole in the wall shop for years now. i get great service, get greated as soon as im there. sometimes i end up talking with him for an hour or more everytime im there. i can call him on the spot and he has what i need. if he cant get it he sends me where i can.
also take some accounting classes in high school and college if you go. you dont have to be the accountant but it will help to know some of it.
And good luck with it all. i hope it all works out for you