Hi Wattie, firstly I'm sorry for your loss!
Those B402 basses are interesting and not super common. I've never had the chance to play one, but hope to come across one someday to try out in person. If you don't have an experienced bassist or guitarist in the family who can evaluate it thoroughly, I would recommend finding somebody who can (possibly taking it to a reputable guitar technician) before posting it for sale online. If you'd like to get full value for a vintage instrument, there will be a lot of questions as there are a ton of things that can hypothetically be wrong that are not easy to identify in photos or even in person by somebody who isn't experienced in guitar maintenance and repair.
If you'd rather not go through the hassle, I would recommend posting it for sale locally on craigslist maybe, so any potential buyer can inspect it in person or you could offer it online as-is, at a lower-than-market-value price to make it worth the risk to potential buyers who would be buying it sight unseen.
In terms of what it's worth, the Reverb online classified website allows you to see completed/sold listings, which is always a good point of reference for uncommon guitars. Here's a link to save you some time:
https://reverb.com/marketplace?query=guild b402&show_only_sold=true