1. Test it manually to verify that there is acceptance of your product idea. Depending on the idea, you may be able to replicate the entire idea with a website 'facade' and manual back end. Your service time might be a bit slower, but you can set expectations for that. With my business, I wanted to test whether small businesses 'got' the process methodologies I was planning to build into a cloud software. So I tested them as a consultant and contracted with two organizations who would pay me to facilitate them through the process. At the end, I'd know if the process resonated or not and how I might need to tweak it.

2. Figure out the ideal (but not overdesigned/built) product and create a clickable prototype of that. (This can be done very cheaply and I can tell you more about that process if you want.) Then do "demos" for people in your network who fit the target audience. With a clickable prototype you can make it as sketchy or as finished looking as you like. But either way, in less than 30 minutes you can essentially demo the product and get initial feedback - does this resonate, is this something you'd consider using and why/not? I got great feedback this way. And there is no "ask" other than for up to 30 min of your time. Plus, you'll start to build up a list of people who are excited to learn more as you get to the next phase.

3. Build the skinniest MVP you can that will get you validation and provide value to the customer. Then pitch the hell out of it to anyone who will listen. Everyone in your network knows people who might be in the right business/industry for your product. I'd tell everyone what I'm working on and say that I'm looking for beta clients to partner with me in testing the first version. I was surprised by how many people made introductions to other people who they thought would benefit from my product. Some of those went nowhere, but I ended up securing 6 organizations to participate in my beta. In exchange for using the product for 6 weeks and providing specific feedback along the way, I gave them a personal onboarding, rolled out features they requested (that I agreed with) every week, and allowed them to use the product for free forever. I pitched (via web screen sharing) to about 15 orgs in order to get 6. 

Thats as far as I've gotten, but its worked really well for me thus far.

Mamie

Brahm;  The basic blocking and tackling of product/market fit and customer validation are no different for B2B than for B2C - Identify who you think are likely prospects, talk to them, get feedback on your idea, take that feedback and build a mockup/PPT presentation/MVP, present to them again, get feedback, iterate, rinse and repeat.  Remember, when you are dealing with a business you are still dealing with individual people.  Identify a company that you think would make an ideal customer - the best possible fit for your product.  this should be in an industry you know well.  then identify the type of user within that company that is the ideal representative of that company's needs for your product. For example, if you are an expert in the trucking industry (random idea) and you are planning to build the next best thing in tracking employee expenses, then identify the top 3-4 trucking companies you can think of who's employees travel a lot and for whom T&E expenses might be large.  Identify the department that should get the most value out of your product, but don't sweat this too hard, just get a meeting with someone, anyone in this dept. and they can help you narrow your search.  Make sure you are prepared to add value at every meeting/conversation - if you spend your time taking and not giving the door will close quickly.  If you are a developer and your's is a business solution then talk to the business people, avoid the temptation to talk with the IT people - you have to talk with the people who will ultimately make a decision to purchase from you or at least act as your champion. good luck.