Paul was not proudly making up a command of the Lord but was referring to the following:
[Luk 10:1-12 KJV] 1 After these things the Lord appointed other seventy also, and sent them two and two before his face into every city and place, whither he himself would come. 2 Therefore said he unto them, The harvest truly [is] great, but the labourers [are] few: pray ye therefore the Lord of the harvest, that he would send forth labourers into his harvest. 3 Go your ways: behold, I send you forth as lambs among wolves. 4 Carry neither purse, nor scrip, nor shoes: and salute no man by the way. 5 And into whatsoever house ye enter, first say, Peace [be] to this house. 6 And if the son of peace be there, your peace shall rest upon it: if not, it shall turn to you again. 7 And in the same house remain, eating and drinking such things as they give: for the labourer is worthy of his hire. Go not from house to house. 8 And into whatsoever city ye enter, and they receive you, eat such things as are set before you: 9 And heal the sick that are therein, and say unto them, The kingdom of God is come nigh unto you. 10 But into whatsoever city ye enter, and they receive you not, go your ways out into the streets of the same, and say, 11 Even the very dust of your city, which cleaveth on us, we do wipe off against you: notwithstanding be ye sure of this, that the kingdom of God is come nigh unto you. 12 But I say unto you, that it shall be more tolerable in that day for Sodom, than for that city.
Paul shows that he is aware of that saying of Jesus by quoting it also to Timothy:
KJV 1 Timothy 5:18 For the scripture saith, Thou shalt not muzzle the ox that treadeth out the corn. And, The labourer is worthy of his reward.
He may also be alluding to this:
KJV Isaiah 61:6 But ye shall be named the Priests of the LORD: men shall call you the Ministers of our God: ye shall eat the riches of the Gentiles, and in their glory shall ye boast yourselves.
Perhaps that would explain some of his remarks about "boasting" as making his "boast in the Lord".
So Paul would have been within his rights to seek out a person of Shalom and "mooch off them" because he would have earned it with his beautiful feet.
However, Paul was given to boasting though always to make a point. He was "pushed into it" by people giving him a hard time over his qualifications.
[Psa 34:2 KJV] 2 My soul shall make her boast in the LORD: the humble shall hear [thereof], and be glad.
[Isa 61:6 KJV] 6 But ye shall be named the Priests of the LORD: [men] shall call you the Ministers of our God: ye shall eat the riches of the Gentiles, and in their glory shall ye boast yourselves.