Best Way For A General Contractor to Work with Subs- Contracts ?

Hi Guys ,

I have a Texas property that is about to have 34 piers installed to adjust the foundation . The foundation company is smaller and well reputed . They are a smaller outfit , not one of the famous multi million dollar ones . 

He hasn't asked me for a contract and he comes as a referral . I know they do good work . He will be collecting at the end of the job about 6k or so .  

What is the professional way to handle dealing with contractors who do not produce a contract or ask for any money upfront . 

I am finding that good contractors do  not ask for money upfront and there are no contracts being signed . 

I have a guy for each trade and I am my own GC for each property .

Should I make an invoice with the agreed upon scope of work , terms , etc  and have them sign it before hand ?

It might get a little tedious , but if it is the right thing to do I am very happy doing it . 

I am curious what you guys think ? Any general contractors care to share how they deal with their subs ?

Thank you so much !