Bronze Pack Method:
Buy basic Bronze Packs (400 coins), most of the consumable cards (Contracts, Fitness, Healing etc) will sell for a nice profit, though sometimes they won't always sell first time, also keep a watch on the players you get, especially the rare shiny ones as they can sell for a big profit (I've sold a few 90+ pace bronzes from unpopular leagues for 4k+ each), though most normal players won't sell for much, if at all, so you can always keep them to work towards 85m value, this is also a profitable way to work towards Pack King.
59th Minute Method:
This method requires patience, luck, and knowledge of a specific market, all you need to do is search for your chosen cards (ie Gold, Barclays PL) and go to the 59th minute and hope to find some steals, especially as some people don't know the market and may list a player for a real good price, or accidently put the wrong price (ie 10k instead of 100k) and if you're lucky you might capitalise on their mistakes, though I'd only suggest this method if you; know the market you're looking at or you might panic buy on a poor deal, and have enough coins to make the most of the method.
Bronze Starter Pack Method:
To make the most of this method I'd advise you have either a Laptop, or a PC nearby to use the UT Web App.
For this method you'll need to use a second account on your PS3, when starting a team you'll receive a free starter pack, discard every card you receive but send 1 Contract card to your Trade Pile, than on the web app list a bronze card for 1000 Start, 2000 Buy Now, then search for your card on your PS3 and do a trade offer, send the coins you got from discarding and the contract, you'll get around 400-500 coins doing this method, than delete your UT on your 2nd account and make a new club, repeat the method however many times you like.
This method is useful if you're really low on coins, it makes roughly 10k an hour with a laptop, considerably less without.
Development Card Method:
This method is useful if you're low on coins, but the speed of income is slow as you'll need to wait for the cards to sell, what you want to do is buy Gold Contract cards for 150-200 and sell for 250+, you can also do this method with other Consumables such as Fitness/Healing as they sell well as everyone needs them, but double check the market as prices change a lot with Consumables.
General Tips:
If you can, do any buying in the early morning GMT (from 1AM) as most UT players will be sleeping, generally this means prices will be lower.
Make use of the Market during Happy Hour/Jumbo Pack times by buying cheap consumables such as healing cards as people will be selling them as they buy packs, pick up any below 350~ and sell for higher.
Don't waste Coins on Gold Packs, it can be tempting to open one in hope of getting a TOTW or a Messi but chances are you'll get a couple of 75 players instead and make a big loss.
I'd suggest getting the TOTW trophy last, focus on the other trophies before you plunge all your coins in the pursuit of a very rare card.
bron:
UT Money Making Tips - PS3Trophies.org