The single best way to “hook” someone on our wonderful fishkeeping hobby is to have their fish breed. I am a moderator on FishChannel.com, and there are always newbies on the site. I find it amazing that every week or so there is a kid who just got his/her first tank and found baby platies, swordtails, mollies or guppies hiding in the top corners. Often, they immediately get visions in their heads of how much money they will make selling the babies to the local fish store. Usually someone will burst their bubble, telling them the local fish store will not want to buy the babies. Other than guppies, most livebearer young are difficult to raise to adult size in a hobbyist’s tanks.
Baby livebearers aside, it is a very good idea to encourage customers to breed some fish—and to let them know that they can indeed swap certain fish for supplies. Paying cash is not necessary, unless the customer is a serious breeder who can produce good fish on a regular basis. For the occasional spawning of angelfish or catfish, a customer will be very happy to receive store credit. For “serious” hobbyists who can offer consistent, good quantity of angelfish, guppies or clownfish, you will probably have to pay cash.
One piece of information you should impart to customers right out of the gate is that you probably will not be able to buy/trade for their baby convicts or kribensis. These are the two egg-laying fish that most commonly breed in hobbyists’ tanks, and they are not a crashingly good seller at retail. What you can do is to encourage your customers to breed fish you know they can do fairly easily—and that you always are looking to buy. Fancy guppies are the first fish that come to mind, and there are serious guppy breeders all over the country. If they are breeding for shows, they have plenty of culls—and their culls are always worth buying to sell in your store.
Angelfish are fairly easy to breed and raise for a hobbyist (I did it out of a 6-foot by 12-foot space for years) and stores always need good angelfish. Cory cats and smaller plecos and hypostomus also make good fish for the home breeder. On the marine side of the hobby, clownfish are the ones most often raised by hobbyists. There is also coral fragging, although depending on the size of your store and its location, you may saturate the fragging business for the same corals in a short time.
Many pet and fish stores find that putting up a sign encouraging their customers to breed certain fish works very well. And all customers usually respond very positively to the “buy local” aspect of fish raised locally by your customers.