I had a look at your sales items. They seem to be electrical circuits and boxes which are probably just the sort of things where people ask technical questions. And as the buyers will usually be spending several hundred dollars, they probably want to check certain facts first.

I think your best bet would be to do as digital ghost suggests and give a short answer first. Don't go into long, detailed descriptions in PMs.

If the customer wants more info, they will ask.

There is one other thing you can do too. You could write a FAQ page for some of the more common sorts of questions.

And you could build up a list of web sites for more information.

That's what one of my sellers did. Not for electrical stuff, but for sourdough starters, he included a sheet with web sites for instructions, recipes etc. I guess it cut back on a lot of queries.

The one thing I think you'd struggle to do is charge extra for 'consultancy' fees on normal ebay listings.

So just make your replies short, sweet and an overview rather than hours of detailed description.