I know some including me have talked about the Gameshark PSP or some such cheat device. But a lot of devices are limited including the Gameshark which has to be activated by a site that is no longer is there unless you can find the program already installed on an old PC...which is very unlikely. Save Cheats are a different matter, they can work on all models on PSP, and all firmwares including custom firmware.
What are Save Cheats exactly, you know how PSP games create a game saves. But let us be honest not all of us including me are great at all the games we buy and need a little help sometimes. One of the first ones I ever used was for the Sega Genesis Collection. I simply went to Gamefaqs did a title search and there it is. Under the title 4th one from the left, it says Saves, click on it. Simply download the save you want, unzip it and place the folder in the Game Save folder on your PSP and you are done. But what have you done? Simply open up the entire game without ever playing it before. 99% of all the saves stored on Gamefaqs are exactly that. They unlock everything, and to my knowledge, you can only do this on the PSP. I may be wrong about the PS3 and other Sony consoles but I have never tried.
Are there any downsides to this? 1% of the saves don't work for various reasons. Otherwise, they are safe to use and you can get to whatever you want now without waiting.