There's a number of "filling" devices available now. All Chinese it appears ("Kegland" is the Aussie front for Chinese stuff I believe), 'cos basically, if it's illegal or if it all goes wrong, do they care? There's going to be no "consumer protection", so be careful!
The device I use (which is Chinese made!) refused to fill a cylinder with liquid CO2 until I followed advise to put the receiving cylinder in the freezer. Don't know why that works (a freezer is way above the temperature to liquify CO2) but it does. Instructions on paint-ball sites seem to cool their cylinders by venting them immediately before filling (seems wasteful).
Most cylinders will be without dip-tubes (unless they are fire extinguishers). The cylinder should be marked with a strip down it if dip-tubed. I pressurised my cylinder (donor cylinder upright) which gets it up to 57-ish BAR (no liquid), cooled the receiving cylinder in the freezer, then filled it by effectively "pouring" the CO2 in to it (if doing this remember to close the valves or the CO2 pours back in to the donor cylinder when up righted). They get about 90% "full", and I imagine cooling and repeating the filling gets more in, but I've never bothered. "Full" is only about 1/2 - 2/3 really full, but seriously (really) filling a cylinder would be hazardous so be careful of tricks that might allow it. I'd have been happier with some sort of jig to get the cylinder safely up-ended. Use weighing scales to judge how "full" the cylinder is.
Just be careful! The pressures may be lower than a compressed gas cylinder, but 57 BAR (which keeps the CO2 liquid) is still astronomically high, and evaporating CO2 becomes extremely (flesh destroyingly) cold!
