In a bear market, it’s essential to buy well below market value and stick to high-demand features buyers are prioritizing.High Inflation: During periods of high inflation, the cost of materials and labor often increases, cutting into profit margins.

There are tons of valuable posts, learning materials, and great individuals here on Biggerposckets- so this is already a good start.

Can a long-distance investor be considered materially participating in their STR property?  

If there's a material issue with the property, it's not going away if you cancel your agreement, they'll have to deal with it for the next buyer, too. 

Estimating material costs is easier but the labor is tough.

Yes, there is an argument made that they have to disclose anything material, but that is subjective.With that said, a red flag that came up recently for me when investing out of state was when I was in escrow on a property that was purchased just a few months prior.

Supposedly its all the books and materials but without the mentorship.

Any reputable contractor has material accounts everywhere and doesn't expect to be paid for labor S/he hasn't yet performed. 

External is usually where they want to approve the color of the house, types of materials, roofing, landscaping, driveway condition, etc.

Do you have credit cards with places like Lowes and Home Depot that you can use to buy materials now and not need to pay off for maybe 90 days?