One of the easier and less involved ways to make some extra money is to keep two copies of your most expensive frog and then breed them.
If you want to make a little extra, keep a habitat with lots of +happiness items and move the frogs into there for a while before you sell.
While they're sitting in there getting happier, you can have another set of 8 in egg form.
Rinse and repeat.
For more frog breeding tips and tricks, click here
gaming.stackexchange.com/users/None/
Here is a way that I found out.
You need to take the two highest level frogs you have and breed them.
Go to Settings -> General -> Date and Time ->
Set Date and Time.
Go forward two days or more.
Go back into Pocket Frogs and sell all the frogs.
(They should all be matured up.)
Go back to Settings -> General -> Date and Time ->
Set Date and Time and go back in time.
You should make a lot of money and experience over time.
Please note that this might affect some of your other games (such as ones where you gain energy or other things over time) in a way where the game counter becomes longer than it should be.
gaming.stackexchange.com/users/9772/Ipod USer
If you breed high level frogs with low level frogs, you get a lot of XP and if you have a lot of potions, you can sell them for lots of money.
Lower level frogs supposedly hatch in less time for people who can wait.
If you can't wait, I suggest that you download the free pop-up apps to get rare frogs(tribus, glass, chrome, lanterna, etc).
You can also race frogs to find chrome or glass
frogs(I found both)
and if you get 1st place, you can take them and breed for rarer frogs(meaning more money).
gaming.stackexchange.com/users/None/
To earn extra money, you need to breed any frogs you can.
Then take them to the pond and eat a lot of flies - then the frogs will mature and then make them happy and finally sell them.
gaming.stackexchange.com/users/9173/Aa 90
And if you're looking for some free stuff, there is The daily gift, located on the menu The frog puzzle game.
Every time you finish the puzzle, the frog that you played with will be at full happiness and you get a free item as a prize.
gaming.stackexchange.com/users/9982/Frog Lover
I have one.
Go to your device settings and change the date to the next day, go to Pocket Frogs, and get the Daily Gift.
it won't always be money, but I did it and got a rare frog.
possible after-effects
This only works a few times on android.
Also, it may cause the game to crash after you've done it quite a few times on apple devices.
gaming.stackexchange.com/users/35846/frogdude123
Doing a race with a frog that has high speed and stamina will get you money if you come in 1st, 2nd, or 3rd.
Unfortunately, racing costs money, more money the higher level that you are on.
You want to come in 1st or 2nd to get or win back your money.
When you race you can also (when you come in first) win an opponents frog...
MORE MONEY (when you sell it)!
gaming.stackexchange.com/users/None/
Not sure why Ek89005's post was voted down, but it is a decent trick.
Empty your mailbox, then buy the most expensive frog you can (either through catalog or froggiedex - don't worry about "wasting" the money).
Once the frog is able to be placed, click "place" then use two fingers to tap two separate habitats at the same time.
A frog will appear in each habitat.
BONUS!
That expensive frog you'd just placed will still be in your mailbox.
You can then do the two-finger-tap repeatedly as many times as you'd like - fill all 15 habitats if you want.
Sometimes items will randomly change after a placement.
You'll have a ton of green callaina frogs (mostly anura, but some other various ones), "missing" frogs, and flowers.
If you have time, scroll through and see what goodies are there.
If you want to be quick, just place and sell whatever you want. Remember your mail box will be screwed up.
New gifts will be at the bottom, but deleted if you delete or place something that's listed above it in the mailbox.
So, if you get any gifts you want, place those first before doing anything else in the MB.
gaming.stackexchange.com/users/37711/Erin
So I had the same questions
and I used the breeding method with my two extremely rare frogs.
It is a fabulous way to get money and experience but if you are impatient and change the time to skip ahead to when the eggs hatch, DO NOT RESET THE TIME AND DATE TO THE CURRENT DATE.
If you do this then the game glitches and turns all of the frogs back into eggs.
Granted
it let me use all of my habitats as nurseries, it's just something to note if you chose that method to earn coins.
gaming.stackexchange.com/users/148641/Mallory
What are some strategies that can be used to quickly earn money or gain experience in Pocket Frogs? For experience, you can complete awards, however it takes a while when your stamp or potion supply runs low.
How can I quickly earn money / experience in Pocket Frogs?
gaming.stackexchange.com
<ios><pocket-frogs>
gaming.stackexchange.com/questions/7918
gaming.stackexchange.com/users/18/Kevin Yap
Keep two copies of your most expensive frog and breed them.  Both breeding the high level frogs with eachother and breeding in general can get you a lot of money when you sell them. 
Users suggest keeping two copies of high level frogs and breeding them Users also suggest breeding any frogs with eachother