Each sealing is a unique situation and rats are very intelligent
  animals. They can fit through a hole the size of a quarter. At
  [1]Affordable Trapping we've been doing this for a long time and
  OTHER trappers have called us on difficult cases they've had
  that we've been able to solve. Age of the home isn't always a
  factor either. Construction techniques, weather, vegetation,
  water, happenstance can lead to an issue but ultimately, it's
  the cleverness and persistence of the animals themselves. They
  want in and they find a way. Well, I'm not selling here. Just
  saying it's not always the obvious that's the problem but the
  nearly invisible and how you handle an issue like these can
  determine whether you've found a long-term solution, or a
  temporary patch that leads to false-confidence and a returning
  or greater issue down the line. == It's not just the material,
  Paul, it's knowing where to seal. Wire mesh is one of the
  materials but we also use others as well. Some materials are not
  good to seal with, and you see them recommended on the Internet
  on DIY pages. Even not all wire mesh is the right wire mesh.
  They can chew right through some gauges of wire mesh or slide
  through it or push it aside. Lots of incorrect information out
  there and even among professional nuisance wildlife removal,
  there's incorrect information. You can seal a whole house and
  *still* miss the entry points and coming in *after* a homeowner
  has tried to do it themselves can sometimes make it more
  difficult as they've obscured important information, making a
  diagnosis more difficult. Of course I can't blame someone for
  wanting to try it themselves first if they like. We're here if
  they have an issue down the road. And yes, it's good to be an
  informed consumer and ask questions. Yet there's also the right
  time to make the phone calls. I could pull a bad tooth with a
  doorknob and a piece of fishing line but sometimes it's best to
  go to the dentist instead. [and compare services with them too
  of course] She is taking the right approach here. Whatever
  company she ends up going with, (of course I hope it's ours and
  that we meet her needs) she's taking the right approach. == I
  suppose my view is biased - often by the time people contact us,
  they're more than ready. It's possible that people have had
  successes at DIY but from my vantage point, I never see DIY
  successes - I only ever see the aftermath of the unsuccessful
  that we then fix for them. In short, a kind of confirmation bias
  but maybe more of a selection bias. I can't know the amount of
  people who don't call/contact us and what their stories of
  success or failure is, just the ones that do. == You'll be
  meeting with Mike - he's got the eagle eyes and knows his stuff.
  I'm good at back-end business stuff but I can't do what he does.
  Apologies for taking up so much of your discussion here and I
  hope you find the solution that works for you smile emoticon ==


References

  Visible links
  1. https://www.facebook.com/Affordable.Trapping/?hc_location=ufi