I used to but not anymore, I'm afraid.
Not knowing what's causing the problem with gear that might be at a client's premises, I may need to visit more than once and travelling costs can build up.
If I need to dismantle an instrument to diagnose a problem and then I need to come back with spare parts to fix it, for example, I don't feel it appropriate to leave things in a mess at the client's premises. That means I need to reassemble things, only to potentially take them all apart again on my return visit.
It's a long-winded process and one which I don't feel is cost-effective for the customer. I therefore urge customers to bring their gear to me.