Buying from a pet shop is sometimes the only option for people and provided anybody goes in with their eyes open to the potential issues then it is their choice where they get them from. You did say in your other post that you were in discussion with an actual rescue centre - did that not work out?
Aside from potential health issues there is also the bond issue. Usually the piggies are just put together for sale with little to no regard for character compatibility. People get a pair and later find actually the pair don’t get on. They were only getting on in the shop due to being young and scared.
By far not every pet shop pair will have issues, more will live long happy lives together but it’s always something to bear in mind.
I have previously advised you about the risks involved and the exceptionally large cage sizes required to attempt a boar trio (300x100cm). Given the ages of the piggies involved you would be well advised to not attempt to bond them as a trio. Instead leave them living as a pair and a single; or just bringing home the pair and not the single.
Be aware that attempting to bond all three of them runs the risk breaking all bonds meaning the two pet shop piggies in this post also end up falling out (as well as not accepting the single) and you end up needing three separate cages with one piggy in each.
Rescues (Adoption and Dating), Shops, Breeders or Online? - What to consider when getting guinea pigs
Adding More Guinea Pigs Or Merging Pairs – What Works And What Not?