From my own experience freelancing, there’s two ways I know to get hands on experience with Marketo:
Become Marketo Partner
First, you can apply as a Marketo Partner. If you’re a freelancer and you have your own business, this is a valid angle. As a partner, you get 3 months of free access to a Marketo account (at least, I did at the end of 2017). That should be more than enough time to get acquainted (or, even better, get certified).
Ask A Partner
The second way is to ask a partner if you can access their training account. I haven’t done this for Marketo, but it’s what I would do if I wanted to get access. I know several partners that’d be totally okay with this, as you getting trained up means they have another expert they can call in on projects. Also, at least in Salesforce, if you link your certifications to said partner, they often get more points on the partner scale.
Get A Marketo Job
If you’re not a freelancer, the best way is to just land a job at a company that uses Marketo. I think a lot of companies realize the amount of Marketo experts is limited. Personally, I feel that if you understand the strategies and principles behind the software, learning to use the actual platform isn’t too hard.
I first answered this question on hands on experience with Marketo on Quora: