Depends where you live but you can look up what spiders are in your area and which ones are dangerous. For example, in most of the US you only really have to worry about black widows (which are pretty distinct) and brown recluses which have a characteristic violin on them but IME often somewhat resemble the harmless wolf spider, which is common in my area.

I'm pretty good at identifying the dangerous spiders now (i.e. distinguishing brown recluse from wolf), but it took several instances of trapping the spider under a glass and then breaking out my cell phone and looking at lots of pictures.

If your area has lots of kinds of dangerous spiders then it might be more of a pain, though.

She knew the type of spiders they were, but I was only assured after I wasn't bitten for a few days