I mean being liked goes a long way right....
In the case of Bolt you have a guy who as we all know is light years ahead of the "best of the rest" who were basically all implicated/caught - and it's not like they weren't talented athletes. But yeah sure, one "superhuman talent" can overcome that? Just like Lance did right?
But of course Bolt is from Jamaica, has a big smile, dances, poses, eats only chicken nuggets and we all love him - so we let the obvious just slide don't we.
On to Ashford - when you step back, she is one of the most interesting sprinters to look at of all time. Because while basically every guy from that era (including the "great" Carl Lewis) was heavily implicated/caught and so was the most famous woman of that era in Griffith Joyner, Ashford never really had any questions/spotlight/heat and she was arguably the preeminent sprinter of that era when you look at her complete career.
There are a couple of things that support her. First is a long career (7 sub 11 second years and ran between 10.7 and 11.1 for 12). A lot (not all, but a lot) of doping in that era was pretty crude anabolics which basically gave a lot of sprinters physical abilities their bodies couldn't handle. Muscles got too big and powerful for ligaments and tendons and they blew their bodies apart. That's what happened to Flo-Jo and Ben Johnson in particular.
There isn't really anything in her progression that jumps out as crazy like FGJ (like being plateaued as a 10.9-11.0 runner then popping to the 10.6's out of nowhere. She first breaks 11.0 as a 22 year old, within 4 years runs 10.79 at altitude in CO Springs (same day as Calvin Smith broke the WR so it was good for sprinting) and that propels her into her career peak which tapped out at 10.76 in Zurich a year later. So in terms of career numbers, nothing jumps off the page as seeming ridiculous (like Fl-Jo, or Marcel Jacobs, or ahem Usain Bolt 10.03 to 9.69 anyone?) Visually she passes the eye test. There wasn't really any dramatic change in her physique throughout her career either.
Now all that being said - it could mean nothing. She may well have been as dirty as anyone in that era - maybe her body just (fortunately) responded in a different way and didn't project many of the major tell-tale signs like it did with others. We simply can't discount anything. Either way I personally like to think of her as one of the "most likely to be clean" out of a tough era to contextualize. That doesn't mean I am fully convinced she was - it just means that I think irrespective of anything she was the most naturally talented of the crop (a similar situation to Bolt, Armstrong etc etc).
Guess we will never know.