Ditch the civic or repair?

I own a 97 Honda Civic Del Sol Si, a stock 5 spd, 134k, very well taken care of, runs awesome, & gets consistantly 35+ mpg.
My sister and I have been the only owners/drivers. She used it as a daily driver up to 113k up here in the Northeast.
For me I use it on longer trips, nice sunny days, give the tacoma a break.
Last summer I had the timing belt, water pump, a bunch of work done, etc.
I always had a friend's shop work on it getting it checked over due to its age, Salt etc. Didn't want to waste $$. Been going there for 5+ yrs....
******** THE DRAMA******************************************

His business was small & he was more involved.
Now he built a brand new shop, is not that involved & has a service writer "chris".
Last summer when I did the timing belt I noticed the rear bumper sagging due to rusty support & asked for estimate.
"Chris" said they would get back to me. Honestly I forgot about it.
Then a month ago I get a vm from "chris". Blah blah blah we are sorry & am catching up on estimates am I interested? Leaves 3 msgs.
So I call "chris" back,we agree on price including a 1/2 hr check over since the car will get taken apart to replace the support.
My usually get ready for Spring routine.
Later the owner, Nate calls me letting me know the car is getting old, rust etc. also belts needs adjusting.
So I ask, is it inspectable? He says yes but is kinda weird on the phone but agree to inspect & fix belts.
Later in day no phone calls wait til 5 go pick up & car is not inspected.
"Chris" says there are holes above each rear tire (by the back bumper they just fixed) so cannot inspect it. Will cost $300 to fix. I'm pissed.
Why is this the first time I am hearing this, I just spent $300 on the rear rear support? Just an I don't know stupid look & Nate's not around.
"Chris" then says he would buy it for $1500 as it sits. He'll fix it up & make $.
I am like what? Where is this coming from? I didn't ask if you wanted to buy it...you guys did $$$ last summer plus this $300 on car that is not "inspectable". Now I am really po'd. But stay calm, pay, leave.
Called Nate on his cell phone only got vm left msg no call back.
Everyone knew my number when they want the work!
Other friends says this has been happening more and more since new shop started.
So whatever we will see each other in passing because we run in the same circle right now want a solution more than an argument.

****************** END OF DRAMA *****************************
Yesterday I emptied the trunk & there is small area on each side in the upper rear wheel wells that rusted thru.
It is like where the rear quarter panel seams meet the wheel well.
Will take pictures after it stops raining.

soooo my question is can I fix this?
It doesn't look that bad & the car was undercoated.
Plus the car runs like a champ.
How do I fix it? Bondo from the wheel well? Its in a tough spot on the inside being a seam.
Just sell and cut my losses?
Sell as is?
I am sure someone wants a good mpg car just cannot work on it myself. Sorry so long.... just do not know when its time to stop fixing an older car & mad at myselft for spending $ for nothing.....thanks in advance for any input or ideas.

 

Two days ago I ran into an old neighbor who rebuilds cars & is a mechanic by trade who checked out my del sol free of charge at the shop he has at his house.

Bottom line is my lil MPG buster is still road worthy & then some.
He wired brushed the rust, applied two scoops of bondo, sprayed the patch after it hardened with black undercoating. FIXED for a six pack & $20.

The other shop was trying to rip me off & steal my car
Clete had worked on my car before & said she has easily another 100k.

Soo... what goes around does come around. Clete's family & my family always hung out but loss touch when I moved. Seeing him unexpectedly was a godsend. I will see the other guy in passing soon & will let him know how it all turned out.

 

Glad to hear everything worked out Judy!