Is there a single adjective for "mercenary-like attitude"?

What is a word I can use for someone who acts like a mercenary? Someone who does something only when paid, without loyalty, ruthless and sticking to the contract, even in the case of life and death?

"I would ask my best friend to help us in this project, but I don't trust him. He's not a bad guy, just very mercantile."

Mercantile means more towards merchants, but is there a correct word for mercenary-like?

Solution 1:

If you don't want to use "mercenary" as an adjective, consider "venal". Mercenaries are bought. They have a reputation for fighting for the highest bidder despite personal convictions (if they have any).

venal
adj
1. easily bribed or corrupted; mercenary: a venal magistrate.
2. characterized by corruption: a venal civilization.
3. open to purchase, esp by bribery: a venal contract.
from Latin vēnālis, from vēnum sale
Collins English Dictionary

I see the word as being akin to "buyable"

Solution 2:

The word mercenary is itself an adjective as well as a noun:

mercenary [mur-suh-ner-ee]

adjective

1.working or acting merely for money or other reward; venal.

2.hired to serve in a foreign army, guerrilla organization, etc.

(From dictionary.com)

"I would ask my best friend to help us in this project, but I don't trust him. He's not a bad guy, just very mercenary."

Solution 3:

The relationship is transactional (OXD)

Relating to the conducting of business, especially buying or selling.

‘a purely transactional relationship’