What to ask? How to not get scammed?

1) What questions are a must ask to not get scammed by SEO agencies? I have gained a basic but solid understanding of SEO through podcasts and studying but I am still having a very hard time with hiring a agency for my company. Every time I book a meeting it is either they do not align with what I learned or they are lying and saying they do not buy links and even though I want them to say they do I can not get them to and they are lying so I do not believe them even if they were doing correct SEO. 2) How would you go about hiring a agency today? PS: I am learning from grumpyseoguy podcasts so I am pretty sure what I am learning is legit. Please do not flood my inbox with SEO offers because I will be responding to none so you will be wasting you time. Thank you for your time and I appreciate any help.