A vip from a place that does not do scuba fills will not allways save you money some scuba shops will require any empty tank to get a new vip before they will fill your tank even with a current vip. Allso some will not accept a vip from others if it is not a vip from a recognized scuba fill shop.
If it is empty and they see any problem they will charge for a Vip + cleaning, possibly tumbling, and a fill.
I took a bunch of my tanks directly to a certifed hydro facility and they did a hydro tumbled tanks as necessary, cleaned, did a vip required by DOT and included a vip sticker which not all hydro facilities include the sticker. My shop accepted the sticker they provided for air fills only my nitrox tanks required O2 cleaning and a new viz for oxygen clean with the oxygen vip sticker.
There was shop that insisted they sell me the big nitrox bumper sticker tank wrap which is not required by law. But I guess shops can make up there own requirements over and above what DOT and the law requires. I will not do business with those shops. Just seems to be a red flag they may not be totally honest!