I've been in the parts business for about 20 years so can give some insight. As
MarkSnelling says, if you want a risk free experience when replacing a head, you buy it from Roland/A Roland Dealer and have a Roland tech install it. It costs more but you're covered 100%. Many people go that route and I don't blame them one bit. It's the safest option.
There are also many people who have the technical skills to install one on their own and want to save some money or they don't have a local Roland dealer so they come to sellers like us. Installing your own head saves a decent amount of money but it's inherently risky because you aren't covered for any failures. So it's up to every shop to make their own decision on how much risk they're willing to take. I can tell you that I've sold multiple 1000's of heads to this type of customer over the years.
When we became successful at this, many copycats started coming out of the woodwork looking for a quick buck. The downside to customers is our competitors aren't as upfront about the inherent risk as we are and in fact even lie to customers saying there is a "1 year head warranty" when not even Roland gives a 1 year warranty. For some reason the industry attracts crooks, so make sure you vet who you buy from first.