Purchasing a production library is an investment. So you really need to carefully consider which one is right for you. One can go for a monthly subscription or a royalty-free buyout. Whatever your choice, it’s great to get free FX from different libraries. It’s a way of sampling without having to spend money yet. So aside from listening to demos, download free FX from production companies are indeed really helpful.
Here are sites that offer free FX tryouts.
You can view direct download links to free FX here