Francisco Terrenos del Caño, Arte o instrucción y breve tratado que dize las partes que ha de tener el predicador evangélico.

Contains details on the instrument and its performance practice.Terrenos describes the vihuela and some of its parts: “shoulder, top, rosette, bridge, pegs and strings” but that not all the parts have to be “played” although guitar players “guitarreros” give little taps on the belly, whereas it is just the strings that should be played.

Tratado III, cap. 4: "aunque más lo riña San Gregorio, que dice que, como la vihuela tiene su espalda o asiento, su tapa, su redecilla, su puente, sus trastes, sus clavijas y cuerdas, no por eso, al tañer, se han de tocar todas estas piezas (que tocar en la tabla sus golpecicos es de guitarreros), sino sólo las cuerdas; y todo lo demás es para que las cuerdas se tengan y suenen bien."

Terminology used: “redecilla” for rosette; “guitarrero” clearly refers to guitar players not makers.
Pepe Rey circulated this passage to the email list “vihue-lista” (27/3/2007) in support of understanding Bermudo’s “musica golpeada” as strummed chords, homophony not percussion, and also the use of guitarrero to indicate a player rather than a maker. Carlos González commented further that the reference seemd not to refer to the way that makers constantly tap and tune soundboards in the process of building instruments.
Pepe Rey provided extensive commentary that needs to be sifted into its corresponding documents.He suggests that terms like “guitarrero” and “violero” were applied to players before they were applied to makers. He notes that "violero" refers to players in early poems (Berceo, Poema de Fernán González) and to makers perhaps only from the Ordenanzas de Sevilla, 1502. In popular language from Salamanca and Extremadura "violero" is the collquial name for “mosquito” (Gabriel y Galán: "los violeros me jacin ronchonis") and obviously the sound of the mosquito recalls more the sound of the bow than the “gubia” of makers. The oldest reference to "guitarrero" known to Rey is in the "Diálogos familiares de la agricultura cristiana" of Juan de Pineda (1589) although it is uncertain to which of the two activities it applies. Pineda (cap. XXVI) speaks of the mechanical trades "que se ordenan para ganar la hacienda" and therefore "privan del privilegio de la nobleza a los que a ellos se dan." He gives examples from classical authors: "Filóstrato escribe que los dados a tales artes viles no eran permitidos tener estatuas entre los victoriosos olimpiónicos, de la cual ley concluye que Teodoro, padre del famoso Isócrates, no fue guitarrero, pues alcanzó estatua en protestación de sus merecimientos en cosas de nobleza." It is even clearer in Mateo Alemán’s "Guzmán de Alfarache" (1604) when he speaks of "lo mal que se compadecían honra y mujer guitarrera", referring to his own wife who "enamoraba los hombres yéndoles a tañer y a cantar a sus casas." Alemán, by the way, was in México and taking advantage of the occasion let me add that throughout all of America, from México to Argentina, the term “guitarrero” is understood, above all, to apply to players. Just look at Google or read Martín Fierro, Neruda, Carlos Fuentes, Lezama Lima, etc. (The mystery to me is to know where they got the term "laudero").

Modern edn: Félix G. Olmedo. Instrucción de predicadores. Madrid: Espasa-Calpe, 1960.
Original book online: http://www.cervantesvirtual.com/servlet/SirveObras/79160620218137506322202/index.htm
For a biography of Terrenos del Caño see galiano2003= http://dialnet.unirioja.es/servlet/articulo?codigo=1147005 (download on Mymac