We are raising or initial funding and we heard about certain ways of deferring retainers or success fees to specific milestones and even exchanging those to a % of equity. Your advice on this matter is greatly appreciated!
There are lots of professional services, even rent and some fixed costs that are possible to barter. If you have a product or service that others went, it's much easier. To simply get a lawyer or financial advisor pre-beta is much more difficult. They need to to believe that equity is going to translate to monetization. For a professional, time = $$.
I was an advisor to a company that traded over $1M of office furniture for advertising with a big Media group. It was a win-win, but you have to understand the ratio's in a deal like this. There is a hard cost to office furniture, very little cost to unsold advertising. The office group leveraged the media at a 3:1 ratio so that every $1. in office furniture, resulted in $3. of media. They used a media buyer to do the deal and it was a win-win. The deal has to make sense on both sides......caveat emptor (let the buyer beware)
There's always likely to be someone willing to do a specific kind of deal, but what likelihood that is depends on how the risk is distributed. As @Steve says, it has to make sense for both sides. And there are many unscrupulous people who aren't up-front about what they really want in trade and may try to trick you.
Now, one would like to think attorneys and financial advisors have to follow a code of ethics. But I think it's rare for a professional services individual to trade their expert services for equity, unless they're a capital investor in the company.
You are specifically talking about two services that are usually billed by the hour. What incentive could they possibly have to let you set a performance standard for them? You either trust your attorney or you don't. This isn't like taking a court case on contingency (if you don't win you pay nothing). Those things are very calculated risks, and as a result reward the lawyer as much as allowed.
I sincerely doubt you will find professional services for barter. If you can't afford the professional services, then you haven't really figured out your business. Start with the assumption that you will never be able to raise a single dime of outside money. How would you change your business plan? Do that. In the long run, even if you have a compelling reason to have others fund your business, if you know how to build it without outside money, you have a far, far more durable business.