There is definitely a learning curve however, I only submit offers for review that I am 100% confident are going to pass their requirements. of the last three deals I've submitted for review two of them have been excepted and one is this still in the process of having the appraisal done.
Also just so you know, they are not Hard Money Lender's they are your joint venture partner in every aspect of the deal. They use their own funds as well as secured loans on their credit through other Hard Money Lender's to help make the deals happen. So you are not using your own credit or your own capital.
The best advice I can give to you if you're going to use them as a joint venture partner is to know your numbers and to make sure that your terms are good enough to give you a way out of any contract without any financial ramifications. But that's what you should be doing as an investor in any all contractual obligations your commiting yourself or entity to.