Advance Payment Guarantee

Q: We are in the construction industry and we use a contract known as an Advance Payment Guarantee and I want to know if this is acceptable please.

Basically, we pay a large percentage of a subcontractor's scope upfront. A third party acts as a guarantor that if the subcontractor fails to deliver (either works or materials) they will pay us back what we have paid upfront.

Please advise if this arrangement is acceptable

Unofficially extending a flat

Q: Sometimes people extend their flats either by one or two extra rooms or balcony unofficially both in private or government setup like DDA flats. These extensions are done at mass level. Nobody is getting harm or any trouble due to this extension. Kindly tell me if this type of practice is allowed in Islam?