Big Agnes & Nemo offer great repair services for their gear (most other brands will just offer warranty replacement, if available).
Poles: TentPole Technologies can repair almost any pole issues, from re-stringing when the shock cord snaps, or entire segments that are broken or too-bent, expect to spend ~$10 per segment replaced or $10 to do work such as re-stringing a pole set
Grommets: These are metal O-ring that you'll find at the corners, where the pole notches into. If they fall out, you can pretty easily repair this yourself with a grommet repair kit that costs <$10. If they fall out on trail, but there is still a hole, that's fine to use with a pole, it's just less ideal since it won't 'notch' on the metal
Zippers: If the zipper track isn't staying closed, this is usually because the zipper slider pull has 'widened' over time & is no longer effectively pressing the teeth together. You can try to take a pair of pliers to 'crimp' the zipper slider on all sides (top to bottom, side to side, applying pressure across the front and back). This can often at least provide a temporary fix for a few trips. Otherwise, if your track has 2 zipper slider pulls, a tailor should be able to remove the malfunctioning one. If you'd like to add a new zipper slider pull, the biggest challenge will be finding one, since gear often uses different, proprietary sizes. Once you have a slider pull, a tailor can add it easily (~$10). If you need to replace the entire zipper track (e.g., you can't find another slider pull or the track is physically damaged), be aware this can be very expensive, expect to spend $50-100. We also recommend seeing a luggage repair specialist, since they may have the larger zippers used for gear, or Narain's & Rainy Pass Repair.
Rips, tears, holes: For small ones, you can stick on a patch of Tenacious Tape yourself. For larger ones, you may need to sew on a replacement fabric patch; most tailors can help with this (if you're doing it yourself, most technical fabrics are rip-stop nylon and this is sold by many fabric stores; most meshes used in outdoor gear however is not widely sold). Remember, sewing compromises waterproofing, since it adds punctures. Ultralight gear with thinner fabrics may require specialists. Two repair specialists are Narain's & Rainy Pass Repair; both accept gear shipped in, expect to spend $30-100
Waterproofing: There are 3 components to waterproofing. It is entirely possible to buy these items & repair yourself, however unless you're treating a spot (in which case Tenacious Tape can work just as well), it can be difficult to get a large piece of fabric back to original performance integrity. (Honestly, this is true even for most manufacturers, who will often ask you to replace the piece that's no longer waterproof.) Rainy Pass Repair can help re-waterproof. As a benchmark, tent-sized fabrics may cost up to $100
- Seam sealant: The seams where the fabric has been sewed together are water-proofed either by a seam tape, or a liquid seam sealant that's applied. With a tape, you may be able to visibly see it peeling away. While you can buy either to do at home, liquid seam sealant is more readily available & easier to use. Seam tape, which is more prevalent in clothing, requires you to match the exact fabric you're repairing, and each fabric has different application settings (e.g., appropriate temperatures to help the tape stick)
- Waterproof coating: Sometimes, the seams are fine, but the fabric fundamentally is losing its resistance to water (you can tell if it's shedding or flaking out white stuff), which is derived from a polyurethane or silicon based coating treatment (different from the coating treatment below)
- Water repellant coating: Called DWR (durable water repellancy), this is a coating treatment (different from the treatment above) that causes water to bead up & roll off the fabric. It can often be applied either as a spray or a detergent that is washed-in (we like products by NikWax or Granger's)
Cleaning & Storing
Gear not in use should be cleaned & dried and then stored loose & in a dark environment, check out our entire protip on the topic here.
We have a general protip on how to store & maintain gear that we highly recommend reviewing as well. If you send us video or a good photo series, we may be able to help you evaluate your repair needs.