the majority of fish that you see in petstores are most like f4 and on....especially sme of the more common things...notin in lfs are f1 unless you can really trust them..
The exception to the rule would be breeding F3/F4 fry from different parents. The goal should be to continually do this...or mix F0 with second and third generation.
Keep in mind that some inbreeding is how we end up with line bred color morphs.