§ 95.33 Cooperative use of radio stations in the GMRS.
(a) Licensees (a licensee is the entity to which the license is issued) of radio stations in the GMRS may share the use of their stations with other entities eligible in the GMRS, subject to the following conditions and limitations.
(1) The station to be shared must be individually owned by the licensee, jointly owned by the participants and the licensee, leased individually by the licensee, or leased jointly by the participants and the licensee.
(2) The licensee must maintain access to and control over all stations authorized under its license.
(3) A station may be shared only:
(i) Without charge;
(ii) On a non-profit basis, with contributions to capital and operating expenses including the cost of mobile stations and paging receivers prorated equitably among all participants; or
(iii) On a reciprocal basis, i.e., use of one licensee’s stations for the use of another licensee’s stations without charge for either capital or operating expenses.
(4) All sharing arrangements must be conducted in accordance with a written agreement to be kept as part of the station records.
(b) [Reserved]
[48 FR 35237, Aug. 3, 1983, as amended at 63 FR 68975, Dec. 14, 1998]
So, a station (presumably a repeater in most cases) may choose either to not charge, or charge fees which cover expenses. Notice that last part about written records. This is what almost certainly prohibits 'open' repeaters, as all users authorized to use someone else's station must be recorded in the station written records.