This was the original struggle and ultimately why EA could not afford to keep making Skate games.
A lot of us have racked our brains trying to think of ways that people would spend money in-game. The problem with buying decks and clothes is that ultimately, EA is licensing those brands and it costs EA money to do that so the profit-margin is minimal. I think that's why that didn't work.
I've yet to hear a legitimately good idea for implementing micro-transactions in the game. I'm someone who bought keys in Rocket League and packs in Fifa Ultimate Team. I'd TOTALLY spend money in Skate games but I just can't figure out a product that's both simple enough to make and be profitable for EA and good enough to actually be sought after by players.