So, early in my investing career, I took a job as the business manager for a GC. I was in charge of new business and estimates. I learned very quickly that people (especially investors) will constantly beat you up over your pricing. The slimeball GC that I worked with had a solution... give a low ball estimate and add change orders as you go to get the price where it should have been in the first place. I didn't like it, but the investors are asking for contractors to get over on them when they will not pay for their time and expertise.
Secondly, I've seen contractors who are so disgruntled over the pay and way that they are being treated, the work becomes sloppy and slow. I've seen contractors who others couldn't have success with do great work when they were treated well and paid adequately. Be careful how hard you tighten the screws on your contractors as it will frequently cost you more in the long run. I can't tell you how many times I've seen investors lose thousands over contractor issues. Time, quality, drama, fraud, theft, etc.
Lastly, I have a client who was doing a flip and after the work was done, the home was broken into, appliances stolen, and vandalized. I visited the property afterward and it seemed too perfect and efficient to be a random act. I did find out that his GC had issues with some of the subs and, although nobody can prove anything, they feel that the subcontractor may have been the culprit. Contractors are not usually the most sophisticated group, pursuing civil cases, etc... they are more likely to sabotage your home as they have the exact toolset for that.
@Jay Hinrichs mentioned a couple of pages ago that the most active investors usually manage their own projects and sub-contract a lot of things. While I've seen this, I have 2 clients who actually have partnered with GC's to be proprietary and have an equity stake in the deal or portfolio. Usually 10%-15%. They work on slimmer margins, take care of service requests on rentals, handle emergencies, etc. on long-term holds. They get the long-term upside from the partnership and know that it's a long-term relationship that benefits them.
I'm not sure at what point it should be a consideration for this kind of thing, but it makes sense to develop long-term relationships with your contractors... especially if you are out of state.
Example: Buy a home that needs $55k in rehab. The value after the BRRRR is complete is around $120k. If the GC does the work at a 10% discount (about $5,500 less) but gets a $12k stake in the property, gets 10% of the annual cash flow, as well as gets paid for ongoing work to sustain the rental property. This reduces your initial out of pocket expense and creates a long-term relationship that will be a big part of your future investments and success.