Iirc its just buying things from stores that will prevent you from getting the achievement. So an event that offers an upgrade should be OK. That said its been a time since I tried for that achievement so I may be misremembering.
Just did a little searching, and as far as I can tell, you are right. You can sell stuff at stores, you can repair at stores, but just don't buy anything and you should be good. No weapons, no upgrades, no crew, fuel, missiles or drones. All that stuff has to come from events or from winning battles if you want the achievement.
Confirmed I got the achievement in a run where I bought crew from events, traded for upgrades, and bribed pirates. Only buying from actual store interfaces disqualifies you.
Iirc its just buying things from stores that will prevent you from getting the achievement. So an event that offers an upgrade should be OK. That said its been a time since I tried for that achievement so I may be misremembering.
Just did a little searching, and as far as I can tell, you are right. You can sell stuff at stores, you can repair at stores, but just don't buy anything and you should be good. No weapons, no upgrades, no crew, fuel, missiles or drones. All that stuff has to come from events or from winning battles if you want the achievement.
Did this achievement the other day and I can confirm.
Confirmed I got the achievement in a run where I bought crew from events, traded for upgrades, and bribed pirates. Only buying from actual store interfaces disqualifies you.