If you want to join a sportsbook, you must first read the overview. Real sportsbook requires a readable and printable license agreement. This is the basis for determining whether each user acts legally and complies with the laws of each country. The license requires the user to complete the terms and conditions without advertisements or changes. you have to know their deposit and withdrawn system. Is there any KYC process?. How much time will need to take withdraw? It is better to join Sportsbook knowing all the issues like what country it is operated from or how it is controlled. You can find out more about these topics by searching online and there are many topics or posts in this forum as well that you can find out about the feedback. If all the requirements are fulfilled then you can apply to this sportsbook.
I believe also that License is one of what we need to seek first and the countries rules about gambling because this will hinder our capacity to enjoy the winnings , it is ok if we will continue losing but once there is a need for withdrawal then it will be the burden.
but the best advise is that Only play in sportsbook that has a good reputation and record specially here in bitcointalk as we have many in this forum that has advertising for long.