I know there are a lot of lenders who charge only a flat fee/origination percentage basically to keep their lights on but everything else comes from the title company. 

Whenever I buy a note (usually non-performing) it has to have plenty of equity on the loan to value as well as a percentage of loan balance.

As for refinancing, a good rule of thumb is that if you can get a whole percentage point lower, go ahead and save yourself the money, but for anything less than that, what you save in interest may be outweighed by what you pay in loan fees. 

One method used is a percentage of construction costs this percentage tends to range from around 4% all the way up to 15+% with the scale of the project inversely effecting the percentage used (bigger projects = lower percentage) after that baseline is established most folks will look back at how long it usually takes to do these projects as well as the client relationship and will adjust accordingly to reconcile these figures.

I'm unsure about the HOA fees, property taxes, insurance, and maintenance fees when it comes to percentages. 

Percentage can be deceiving.

As said above, it you are buying tax liens, most owners will pay the taxes, and you will wind up owning only a small percentage of the properties.

It's done with the understanding that the call is not free consulting, rather more of an interview to determine if my practice and the prospect are a good fit.If a higher percentage of my calls were those focused solely on fees ("price shoppers"), those fishing for free advice, those with not a lot of complexity that I would have to turn down, etc, I might consider charging a nominal fee to like the previous poster mentioned.

The average rate for a thirty-year fixed mortgage during June was just above 3% and dipped even lower in July, almost a full 2 percentage points below where it was in November of 2018.

Do not mix up the basis plus real property improvements with expenses these are two different tax issues.Second property that parents own or family members are not explained what percentage they own, and if there is any rental income?