Specific arrangement depends on your economics. In general though, 4 out of 5 people that would tell you they would be great at referrals ended up not being helpful at all. The ones that did work out well, you would need to dedicate time to build that partnership to produce results.
To structure that relationship, at pre-seed, you can make them "advisors" and sign agreements with results and referrals as milestones. Put an expiration on the time from intro to contract, motivate them to get to contracting, not just get to intro.
In Series A, it's more sophisticated referral or partnership doc with the company (not usually an individual any more), and was ~10% for referred revenue for between 1-2 years.
It's best to think of them as the commission that you would normally pay out for a sales team or BDR team to get the contract done. If the number is too small, it won't be motivating for them to follow through. if the number is too large, you cut your own margins.