The biggies that you don't always see (read expensive) for me in CO are stable soil/foundation/water intrusion, aluminum wiring or out of favor fuse panels, hvac if not replacing, sewer scope in most older neighborhoods, roof (which will need to be brought to code (shingles, ice dams, re-sheeting maybe) on the sale usually if it's older). 

And if the soil tested as unsatisfactory, I just eat the cost of the P&M test?

Underneath, it should show a second box that says Select a sub forum as shown below

Make sure you have good soil that can easily absorb the sewer water, and there is space where you can extend the drain field if needed.

If you can do rock or pea gravel use Engineering fabric underneath it.  

You don't say the lot size or topography but generally So MD soils are not difficult if you're not near water front.

There are a few issues here: 1) you are being pressured by this being a "hot" property- Don't let that cloud your judgment or your business plan; 2) Without full disclosure in the form of property disclosures or an inspection, you really have no idea what this property has going on underneath the veil---- Get an inspection and pressure the selling agent to provide disclosures; 3) If you don';t put earnest money down with your contract or within a few days of your accepted offer (depending on the contract requirements) your offer is not accepted since there is no consideration.

The house has been vacant for a couple of months now and he is interested in getting out from underneath it, as he doesn’t want to keep paying the mortgage.

This happened at one of my old rentals in Tampa and the branch crushed my carport as well as the tenant's van underneath. 

The Phase 1 vendor may suggest a Phase 2 and soil samples to make sure the ground isn't contaminated from the oil tank.