In determining whether a group of persons is or is not a firm, or whether a person is or is not a partner in a firm, regard shall be had to the real relation between the parties, as shown by all relevant facts taken together.
     Explanation 1.--The sharing of profits or of gross returns arising from property by persons holding a joint or common interest in that property does not of itself make such persons partners.
     Explanation 2.--The receipt by a person of a share of the profits of a business, or of a payment contingent upon the earning of profits or varying with the profits earned by a business, does not of itself make him a partner with the persons carrying on the business;
     and, in particular, the receipt of such share or payment--
         (a) by a lender of money to persons engaged or about to engage in any business,
         (b) by a servant or agent as remuneration,
         (c) by the widow or child of a deceased partner, as annuity, or
         (d) by a previous owner or part owner of the business, as consideration for the sale of the goodwill or share thereof,
does not of itself make the receiver a partner with the persons carrying on the business.