Subject says it all.

I believe "excessive" in this case might be subjective. 

Also, with conditions applied such as, 'subject to buyer finance', am I able to back out of the deal within the due diligence period, if I am unable to find an investor willing to purchase the contract?

@Erik Romo If it isn't assumable (very few are these days) just do a Subject To or a Wrap.

Putting a price on the contact list is really subjective so it's hard to determine what might be a fair value.  

This is a subject thats widely debated in the REI community. 

Even allocating a portion of the monthly rents towards the down payment is an exposure.Each State can have unique issues with this approach, so you should ALWAYS get legal counsel on this subject and  how to draw up the agreement. 

The subjection property could have been built in 2015 or 1915.  

If so, then yes. there may be a tax advantage (subject to other income limitations and issues) for depreciation, utilities, mortgage interest, property tax, etc.If the house was not available to rent, then it was not "in service" yet, and there would be no tax issues.

You could look up the subject on here which is where I read about it.