Listed sizes indicate the range of size in 'TL' (total length) for the listed species as measured from smallest to largest of the actual current stock and are guaranteed to be within 1/16th +/- of an inch of accuracy. Most fish will be somewhere between the listed size range and the fish will never be smaller than advertised size (within 1/16th +/- ).
Size matters and you always get what you pay for!
The size matters for a few reasons besides the obvious reason, so that I can list with a size and of course price accordingly. If you order for example a 1" fish and you are shipped a 3" fish what happens if your current tank inhabitants are 1"? They may become snacks for the new 3" fish because they are sized incorrectly and are now incompatible. The same applies in the opposite situation and that would be bad of course. Also, you need to get what you paid for. This is especially true when receiving undersized fish when you've searched and paid for a larger size. So, no eyeball measurements here. Every single fish that comes in is put on a ruler(the same one) during the unpacking process for size check. This is when I am looking for the largest and the smallest of the group and then where the rest of the group fall in place. When a species is listed for example as 2 - 2.5" then it is confirmed by me that the smallest of the group was 2" and the largest was 2.5". Often most will land somewhere in between the two numbers. Other times, it may be heavy to one side of the measurement over the other. Meaning more may be closer to the 2.5" size or more may be closer to the 2" size. With in most cases, only a 1/2" difference between the listed range it is almost unnoticeable and this is particularly true on larger fish. Then during the order packing process I take the time to measure every fish that I ship out to confirm the size is correct and it also help me monitor any sudden but usually small growth spurts that do indeed occur.
The #1 complaint is see (not only from me) is on undersized fish. Particularly on smaller fish in the 1" range. I have received emails stating: "I ordered 1" fish and you sent me fry". The email is a true story however the complaint was proven to be incorrect.
So how big..err small is a true 1" fish? Very small! Yep, not much bigger than a pencil eraser. That said, on smaller fish every 1/2" in length can look drastically different as with the length they often grow nearly that in height as well. This is less noticeable the larger the fish become. Then we have to compare species to species. For example, a 1" oscar 'appears' larger than a 1" Geophagus. How so? Oscar's are rounder & taller bodied looking more robust than the thinner, laterally compressed bodies of a Geophagus. So, a 1" oscar will give the illusion that it is larger then the 1" Geophagus.
My size guarantee is if the fish is under the smallest listed size by more than 1/16th of an inch than that fish is free!
How do you prove it? Well the receiving party must do the same as I do, put them on a ruler, send me clear photos showing the exact measurement and if the fish is indeed undersized by more than 1/16th of an inch I will credit you back for that fish. So far, I have never had to issue credit because of undersized fish. Measuring every individual fish is a long process. Especially when a new import lands containing 1,000's fish at a time. However, it is a job requirement that is necessary to provide you with exactly what you've paid for. As mentioned above I also measure every outgoing fish for size confirmation and to keep track of any growth. Any species that remains here unsold is pulled and remeasured roughly every 45 days to check for growth and the listing is adjusted appropriately. Some species grow faster than others and the sizes sometimes change rapidly so I do my best to stay on top of being as accurate as possible. Sometimes you may see a listed size never change. Often that is because I have replenished the inventory with fish of the same size when the already listed inventory was getting low.