check_availability checks for each record whether it is available for direct download (can be downloaded instantly) or not (and thus must be ordered before download).
check_availability(records, verbose = TRUE)records data frame, containing one or multiple records (each represented by one row), as returned by get_records
logical, whether to display details on the function's progress or output on the console.
A data frame of records (as defined with argument records), extended by a column download_available (logical).