First, agree with post #2 that there are two sides to this coin. Legal and tax.
I make it very clear, in writing, that I can only consult on the tax side, and that they should consult a business attorney for the legal and asset protection side.
Second, tax entity structuring consulting engagements are good engagements. You should absolutely charge for your time. Create a consulting engagement letter that names both your client and his probable future business partner. The key is to make it very clear in the engagement letter what you're consulting on, and that the decision of what path the clients take is ultimately up to them, not you.
Usually I ask for projected financials and projected 1040 data so I can run an effective tax rate calc, and then a phone call to dive deep into the pros and cons of each tax entity, as well as what they anticipate will be the life cycle of the business, and how each tax entity will behave at each point in the life cycle. Things to consider are allocations partnership vs S Corp, an S Corp's affect on QBI both positive and negative, appreciating assets inside of a corp, etc.
The point is, good advice is very valuable here, and you should therefore charge for your time. How many times do we see a prospect that is in a tax entity he or she shouldn't be in, because they either read some articles online and DIYed it, or took the advice of an inexperience bookkeeper or tax preparer? Getting it right from the get-go saves the client much more money than what you'll charge.
The good news, if you impress them with the tax entity structure consult, you're almost certain to pick up all of the compliance work (entities and 1040s), plus the bookkeeping if you offer that.