Started a company that sells SAAS to US investment banks. I was a former banker and spent a lot of time priming my colleagues for the service prior to starting it assuming they would be willing customers when it was ready (we addressed a niche that was quite a problem for the banks). I thought that if we built a better mouse trap that significantly improved the user experience (for investors, the under writers and the issuers - the companies that actually raise the money) and saved everyone thousands of dollars it would be a no brainier for the banks to use us. Didn't happen. When the time came, bankers who, contrary to public perception are highly risk averse and focus on risk mitigation, didn't want to migrate to something untested despite our domain knowledge and demonstrable improvements. They didn't say this of course - it was always another reason such as "it's not my choice" or whatever.

The way we established a foot hold was to go straight to the issuers. What made our service unique is that while a bank was our user the service was often chosen on behalf of someone else (their client, the issuer). 99% of the time the issuer is silent on which service the banks use, after all they pay the banks to advise them. So we instead sold the service to them (well in the beginning let them use it for free). They in turn told the banks that they needed to use our service and the banks, who ultimately serve the issuers, simply complied. Once we had 2-3 of the banks onboard, network effects kicked in. With each sale we would go to another bank and say "let me show you what we did for XYZ"

Moral of the story (for us at least):
1) someone may indicate they are a champion but when the time comes, most are unlikely to be there. For every team of 40-50 you can at best expect 1-2 people willing to be champions
2) if possible (and I can appreciate that not all services can do this) sell to the person that ultimately benefits from this. In our case, banks use our software in relation to capital markets deals for other companies like John Deere so go to John Deere directly.
3) random point not mentioned above but worth highlighting ... I find that enterprise customers care more about making a dollar than saving a dollar. Our sales improved dramatically by tweaking the message to focus on this. If possible, focus on how you help these organizations grow P&L
4) I am a HUGE believer in Trojan Horses (and I don't mean hacking software). If possible, figure out a way to get your prospects using or benefiting from your software immediately by giving some service away (maybe not even your core service) weekly or if possible daily. The more they interact with you, the easier it is to bridge the divide and get through the process.
5) last point, don't get hung up on engagement letters. I know the lawyers will advise against this but a lot of deals die in the engagement letter phase. I appreciate not every business can do this but I made it crystal clear to my accounts that if they don't like my service they don't need to pay for it - that gave gem the comfort to use it regularly and at the end, they all paid for every use.

I can go on further on some of the tactical nuances of the above and other strategies. Feel free to ping me.