Del. Code tit. 30, § 6203

Accommodations intermediaries are responsible for collecting and remitting the short-term rental tax under § 6202 of this title unless the accommodations intermediary has a contractual arrangement with a hotel, motel, tourist home, or other accommodations intermediary, licensed under § 2301 of this title, to collect and remit tax in accordance with this chapter. The short-term rental tax must be collected no later than the earlier of the final payment of all rent due or occupancy of the short-term rental. If a short-term rental stay is cancelled in whole, or in part, the cancelled portion of the stay must not be subject to the short-term rental tax and any amount of tax collected for such cancelled portion must be refunded.