Looking in the OED, I see support for the wine-cask-piercing tool origin, but not for the origin clearly involving one in charge of an auction. There is a connection to wine selling, and this might be close to what you are theorizing.
Etymology: Middle English brocor,
-our, brokour, < Anglo-Norman brocour (also broggour) = Old Northern French
brokeor ( < Latin type *broccātōrem),
nominative brokiere ( < Latin
*broccātor) of which Godefroy has one example explained by him as ‘celui qui
vend du vin au broc’, as to the
precise sense of which see below. The
Central French equivalent was
brocheor, brochière; and the word is
the agent noun of the Old French vb.
brochier, Old Northern French brokier
( < Latin *broccāre) in the sense ‘to
broach’ or ‘tap’ a cask. Brocheor,
brokeor stand in precisely the same
relation to the n. broche, broc, and
the vb. brochier, brokier, as tapster
or rather the earlier tapper stand to
the n. tap, and vb. to tap in
Teutonic: the brocheor, brokeor,
brokour, or broker, was lit. a
tapster, who retailed wine ‘from the
tap’, and hence, by extension, any
retail-dealer, one who bought to sell
over again, a second-hand dealer, or
who bought for another, hence a
jobber, middleman, agent, etc. Compare
sense of Latin caupo.
The Romanic vb. broccare was evidently
< brocco, brocca in the sense of
‘spike, piercing instrument’ ( < Latin
broccus, brocca adj.: see broach n.1).
But these nouns appear to have
afterwards had their sense modified
from the verb, so that in the Old
French vendre à broke, or à broche, in
modern French vendre à broc, the sense
passed from ‘broach’, to ‘broaching,
tapping’, and at length to ‘the
quantity of wine drawn at a broaching
or tapping’, and hence ‘the jug or
vessel which held this’, as in modern
French broc (from 5 to 10 litres).
Anglo-Norman had also a derivative
form abrocour, and there were
Anglo-Latin words abrocator,
abrocamentum; also brocarius
‘proxeneta, interpres et consiliarius
contractuum’, and abrocarius.
Brocarius appears to have been formed
on the n. (broc(c)a, broc(c)us);
abrocarius must have been formed on
the apparent analogy of brocator,
abrocator.
The earliest usages have already lost any connection to wine tapping or selling.
1377 Langland Piers Plowman B. v.
130 Amonges Burgeyses haue I be
dwellynge at Londoun, And gert
bakbitinge be a brocoure [C. brocor]
to blame mennes ware.
1393 Langland Piers Plowman C. vii.
95 Ȝut am ich brocor of bakbytynge ·
and blame mennes ware.
1582 R. Stanyhurst tr. Virgil First Foure Bookes Æneis i. 14 For gould his
carcasse was sold by the broker
Achilles.
Best Answer
Some words are barely changed over the centuries, like 'mother'. Some words are mashups of mashups and this is one and 'handkerchief' is one.
Yes, as you noted it comes from 'hand' and 'kerchief', and 'kerchief' comes from Old French couvrechief for 'cover-head' ('chief' and 'cap' and eventually 'head' are related also back to Proto-Indoeuropean).
But that's backwards. Forwards, the current word is pronounced /'hæŋ-kɾ-tʃif/, which, as far as most English spelling goes with pronunciation, is fairly close. But in actual use, it has been shortened to 'hankie' /'hæŋ-kɪj/ and signifies something to blow your nose with.